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The Common Cold
The Common Head Cold:
 Colds In General

 Anatomical Outlines

 Nose And Throat Functions

 Highways For The Invasion Of Disease

 Predisposing Causes

 Atmospheric Factors

 Colds And Micro-organisms

 Symptoms, Complications And Sequelae

 Principles Of Prevention

 Methods Of Prevention

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Atmospheric Factors

( Originally Published Early 1900's )

There has been, in the most recent times, a tendency to deny the influence, or at least minimise the importance of atmosphere in the causation of colds. This tendency is but the outgrowth of the modern doctrine of the bacteriological causation of colds, for it seems to be one of the weaknesses of the usual habits of reasoning that the mind, dominated by one idea of the causation of a thing, can only with difficulty entertain a just appreciation of other causes.

The medical as well as the lay mind has become obsessed by the idea of colds being due to the action of micro-organisms. We find on the one hand an over-emphasis placed on the contagiousness of colds, and an over-dependence on the vaccine treatment and local use of antiseptics; while on the other hand, too little weight is given the matter of general health and body resistance, with an attitude of indifference or contempt for weather influence.

Frequently we read or hear that it is a mistake to suppose that colds have anything to do with cold weather, and that a draft cannot do harm because it is nothing more than a concentrated dose of fresh air which should be at all times welcome. But when we reflect upon our personal experiences, we know that a close or humid atmosphere gives us a sensation of stuffiness in our nasal passages. We have a vivid remembrance of the running from our noses on cold, bleak days. We feel obliged to associate with drafts the almost certain tendency to sneeze, and we have all had the disagreeable experience of a cold in the head, tonsillitis or laryngitis following some indiscreet exposure to bad weather conditions.

We are not, however, obliged to depend upon mere personal impressions and conjectures as to the effect of weather in the causation of colds. Tables dealing with a large number of cases of acute inflammation of the respiratory tract show an increase in the winter months, especially with cold, humidity, and high variable winds. The most impressive statistics I have seen are those of Professor Schade of Kiel, taken from observations in the German Army, just before and during the late war (Zeitsch f.d. gesampt. Medizin, Berlin, 1918-1919, VII, 275). His data are based on an analysis of three-fourths of a million cases of diseases of the upper air passages in the army during peace time, 1900 to 1912, and a more de-tailed study of 17,000 soldiers in the trenches of their western front in 1914 to 1917. The outstanding fact brought out was that those cases coming under the general appellation of "Colds" in-creased regularly with the falling of the thermometer, and there was striking parallelism in their number with the number of cases of freezing and frostbite. So-called colds were from two to three times up to seven to eight times more frequent in winter than in summer, and in the winter of 1916-1917, marked by excessive cold weather, the number was three times greater than in other winters.

Supplementing statistical proof of the influence of certain weather conditions, we have the evidence also of experimental procedures. Animals have been exposed to atmospheric conditions which duplicated those in nature supposed to be especially productive of colds. Lode's experiments were with animals infected with the pneumococcus, and with one-half of the body shaved. After being given a warm bath they were exposed before an open window. The result was infiltration of the lungs, which sometimes was even fatal. Durck got the same results with animals dipped in ice water, after having been warmed in an incubator. Flourens got pulmonary hyperemia and bronchopneumonia in birds after severe exposure to cold. Aufricht saw inflammatory changes in the lungs as the result of animals exposed to cooling process. Nebelthau and Zellisen got infiltration of the lungs, and in some cases pneumonia. Jezersk's experiments differed from those previously made, in that they were milder and more nearly approached our real experiences. He did not use such severe cooling methods, and did not with-draw nature's method of protection by shaving the animals. He found that by cooling an already moist, uncovered part of the chest in the case of rabbits or goats there occurred always some changes in the lungs, from simple engorgement to more marked disturbance.

All these experiments are supposed to have been conducted in a scientific manner, and comparison made with control animals, in which the atmospheric factor was omitted. Lode, for example, found in the case of his animals infected with pneumococcus, either subcutaneously or by the inhalation of the powdered culture, that the mortality was 85 per cent for the animals exposed to the cold, and only 12 per cent in those not exposed.

It is not necessary to deny the bacteriological causation of colds in our advocacy of the importance of the atmospheric factor. Both are essential exciting cause's.

There are some very natural grounds for assuming an atmospheric influence. We live at the bottom of an ocean of air covering the whole surface of the globe to a depth of about 150-200 miles, having a total weight of five quintillion tons. Though it is immaterial to our senses except when in motion, physicists tell us that the air is made up of molecules the size of one millionth of a millimeter, so small in fact, that according to Kelvin, Maxwell, and others, one cubic centimetre contains twenty-one quintillion. These infinitely minute particles are in a constant state of turmoil, and the number of impacts to which each molecule is subjected is something like 4,700,000,000 per second.

We inhale a volume of the stuff, amounting, according to Professor Foster, to 2600 gallons in 24 hours; this is about 34 pounds by weight as against 5.5 pounds of food, liquid or solid, which is taken into the body in the same length of time. As above noted, we may go for a number of hours without water and for a number of days without food, but deprivation of air for only a few minutes, makes the difference between life and death.

Air is at the same time the most constant and the most variable medium, being constant in its chemical constitution, but exceedingly variable in its physical. The mixture of oxygen, nitrogen, and carbonic acid gas, of which it is composed, maintains a most remarkably constant proportion, but we need not to be told how greatly the air may differ in its temperature and content of aqueous vapor, and how suddenly these changes may come about.

Huntington, in his interesting work entitled "World Power and Evolution," goes back to the earliest geographical eras, to emphasise man's dependence upon climate, which he avers has been the most important factor in his evolution. The great development periods of animal life, he says, coincide with colossal climatic crises, the most noteworthy being the cerebral development which characterised the glacial period. Man, in his struggle against the handicaps of Nature, evolved into a being, dependent upon atmospheric environment, and in the end delicately adaptable to its variations.

To enable us to utilise this vital medium for the nutrition, growth and development of the organism, Nature has given us the respiratory apparatus. This apparatus consists of an elongated pathway, which we may look upon as an invagination or dipping in of the surface membrane modified into a moist, delicate lining and provided at each extremity with specialised organs. At its pulmonary or innermost end, we have the air cells concerned only with the chemical properties of the air. At the outermost, or nasal extremity we have the erectile tissue concerned only with its physical properties—its temperature and moisture.

Is it not axiomatic that any organ of the body is especially susceptible to the influence of the agent or medium to which it is particularly adapted The eye, made to receive the rays of light, will be damaged by an effort to utilise poor light, or by ill-directed rays. or excessive light. The ears will suffer from exposure to unnatural sounds. The stomach becomes disordered by abuse of the amount and kind of food put into it. Therefore, we may expect the air-tract to be injured by certain abnormal conditions of the atmosphere.

Let us consider especially the nose, because it is here that colds most frequently occur and nearly always begin. It is the nose that we have to consider as the special seat of a cold; its winter quarters, so to speak, in winter; its watering place in summer. Here, therefore, is the best place to study the phenomena of cold-catching.

It is the business of the nose as a respiratory organ so to modify the inspired air that it shall acquire a warmth and moisture acceptable to the lungs and suitable to the proper functioning of the organs. Irrespective of its temperature the external air is brought up nearly to body temperature, and irrespective of its state of humidity it is brought up to the point of saturation. This work is done as indicated above in the nose and is made possible by the presence of the so-called cavernous bodies, constituting the erectile tissue of the mucous membrane, a net-work of interlacing vessels embedded in fibrous tissue containing many elastic and muscular fibres. Innervated by the sympathetic nerve fibres, this erectile tissue, by virtue of its responsive vasomotor connections, can become suddenly congested and swollen or anemic and contracted according to the particular atmospheric need.

The nose, being that part of the respiratory apparatus especially concerned with the physical properties of the air, should be particularly affected by abnormal conditions of temperature and humidity. In its effort to adjust itself to the varying physical state of the atmosphere, it is sometimes put to a very great strain. The temperature of our environment may change not only from day to day, but even from minute to minute, when we add to the changes incident to nature those that are of artificial making. To go from an overheated apartment suddenly to the cold outside air, or vice versa, is to make no small demand upon the nasal organ in the way of climatic adjustment.

In the matter of moisture also, a very great burden is often placed upon the circulatory and evaporating function of the nasal organ in order to bring inspired air up to saturation. Leonard Hill, the great English physiologist, has pointed out that at 30 degrees Fahrenheit, a cubic foot of air holds 1.9 grains of watery vapour, and when warmed up to body temperature it holds 19 grains, and he states that in quiet breathing the ordinary individual breathes a cubic foot of air every four minutes.

Since we have learned in discussing the physiology of the nose that the outside air, no matter what its temperature, tends to be brought up to body heat, it is evident that every individual breathing quietly air of a temperature slightly below freezing, must in four minutes, loose from his nasal membranes the difference between 19 and 1.9 grains or about 17 grains of watery vapour.

Roughly speaking then, in one hour's time there would be a loss of about half an ounce of watery fluid. Taking active exercise it is said a man will breathe a cubic foot every 1-2 minute, so that under the circumstances the amount of watery secretion given off may be as high as 2 or 3 ounces, in the course of a single hour.

It is evident that a heavy task is sometimes demanded of the nasal functions, and we should be able to understand why the nose is especially liable to be affected by atmospheric conditions, considering the great strain it is sometimes put to, in adjusting itself to extreme temperature and humidity states and to sudden variations in these properties.

Better to understand the reaction of the nose to atmospheric conditions, it is necessary to consider this organ from still another standpoint. The nose, besides its functions as an organ of olfaction and respiration, has a certain rôle to play in the heat regulating mechanism of the body. In the performance of this function it comes into intimate relationship with the function of the skin, and it is necessarily responsive to stimuli reaching it from this source.

Man maintains a constant temperature within, notwithstanding the fluctuations of the outside air. His temperature does not rise and fall with it as does that of fish and amphibia. Heat regulation is a matter of heat elimination, not of heat production. The myriads of cells of the body, like minute furnaces, are forever producing heat which if there were no outlet would have the body in 36 hours at boiling point. Elimination is constantly in progress, but by means of its marvellous automatic thermo-regulatory mechanism, the body is made adaptable to changes of the outside temperature so that there shall not be an undue abstraction in the presence of extreme cold.

As stated above, the chief organ of heat elimination is the skin, which, by virtue of extensive surface circulation and gland supply, responsive to cold stimuli, may allow a great or small amount of heat to escape by the process of evaporation and radiation.

A certain definite part of this function of heat elimination is performed through the respiratory organ. In some of the lower animals the respiratory outlet is of great importance, as is evidenced in the panting dog after exercise. In man, about one-sixth to one-fifth of the elimination is through this outlet; 23-20 per cent as compared to 77-80 per cent by way of the skin.

This relationship varies with the temperature of the weather in a certain definite way. The colder the outside air, the less the elimination from the cutaneous surfaces and the greater from the respiratory tract.

When the external air is cold the cutaneous vessels contract, lessening the activity of the sweat glands, and hindering elimination both by radiation and evaporation. And it is during cold weather that the elimination would be naturally greater from the nose, because the nose in the performance of its respiratory function gives off more heat the colder the air.

We must assume an intimate relationship through sympathetic nerve connections, in order to have a regular co-operation in these functions. Lessened cutaneous activity means contraction of the superficial vessels and determination of the blood to the internal organs. Increased physiological. activity of the nasal organs means quickened nasal circulation and greater need for a supply of blood to the vascular erectile tissues.

There is, therefore under ordinary circumstances, a nice relationship and apparently a perfect co-ordination of the functions of the nose as an adjunct to the heat regulating function of the skin, to its functions as an organ of respiration. Under circumstances of extraordinary weather conditions, these relations may be disturbed and these functions upset.

Climate marked by an air that is cold and dry is by universal consent most desirable. The heightened physiological activities of the nose under these circumstances, giving up equally increased warmth and increased moisture, conform precisely with the atmospheric conditions for air that is dry as well as cold.

In an atmosphere of low temperature and high humidity,—the cold damp air of most renown for its cold producing effects, the respiratory function of the nose does not conform so perfectly with the heat producing function. The reason bad weather is bad is that the nasal functions are in a certain way bound up with the heat regulating operations of the body, and therefore under the influence of impulses originating in the skin.

The nose is responsive to atmospheric conditions, particularly to temperature and moisture, not only because of its respiratory functions, but also because of its heat regulating functions and in the latter instance, the responsiveness comes indirectly by way of the cutaneous organs.

It sometimes happens that the demands made upon the nasal organs in connection with the latter functions are in conflict with those of the former.

Just to what extent the nasal organs are de-pendent upon the skin for its consciousness of temperature variations, we are not prepared to say. The cutaneous surface, we know, has a well developed thermal sense, more marked, as Goldschneider has shown, for cold than for heat. Unfortunately, it is not provided with nerve end-organs for distinguishing degrees of humidity. The skin, therefore, is not capable of taking into account disproportions both in the temperature and the humidity of the atmosphere, and it so happens that the reactions upon the nose, arising from cutaneous thermal stimuli, are not always consistent with nasal respiratory function.

In the light of these facts, what shall we say about drafts and how explain their supposed influence in precipitating colds? Is there a rational basis for the widespread fear of a draft, or shall we regard the popular dread of it as a ridiculous obsession which should not be entertained?

A draft may be defined as a current of air at a lower temperature and greater velocity than the surrounding atmosphere, impinging upon a localised area of the body. It is the general opinion that it is particularly harmful to a person sitting quietly in a warm, stuffy room or in any place if the body is overheated, and especially if in a state of perspiration.

We believe that herein are given conditions which, according to our theory of cold-catching, we might well expect to bring about an attack In the first place, when the cold air hits a restricted area of an otherwise warm body, the effect is to interfere with nature's effort to bring about the necessary heat elimination by way of the skin. In the next place the cold air acting through the sympathetic nerves causes a determination of blood to the erectile tissues which is contrary to physiological needs, for the individual is at this time in a warm environment breathing warm air.

The result will be the congestion of a disturbed function and if the irritation continues, and the supplementary factors,—micro-organisms,--are not lacking, this must eventually result in a cold.

The avoidance of drafts we maintain, therefore, must not be considered as arising from an ignorant superstition, but rather as a very wise precaution, having a good scientific foundation.

From the atmospheric standpoint, the conditions favourable for contracting colds occur when the air felt upon the surface of the body differs in temperature from that breathed, particularly if at the same time, there happens to be an unusual disproportion between the temperature of the air and its relative humidity.

Cold is a more powerful stimulus than heat, and the cutaneous nerve end-organs sensitive to cold are more numerous than those for heat. Cold acts as a positive stimulus which sets up an active contraction of the vessels of the skin, in distinction from heat, which has a negative or passive effect and is attended by a distention or relaxation of the vessels.

We all concede the invigorating effect of exposure to cold weather and the wholesome, energising effect of cold baths. But in order that cold shall have these good effects there must be normal responses, good co-ordination of function and adequate reactions. Under these circumstances, the cold acting upon the cutaneous vessels causes their dilatation. And when there is increased supply of blood to the nasal organs, it is seen to be in exact accordance with the physiological needs. When, however, the cold occurs under the circumstances we have mentioned as especially conducive to colds, the determination of blood to the nasal organ is contrary to physiological requirements, and we have a passive congestion instead of the normal, active flow of blood.

This idea of the effect of cold in the causation of "colds" is quite different from the old theory often quoted, which explained them as due to the contraction of the cutaneous vessels driving the blood to the internal organs, including the respiratory tract.

Heightened functional activity demands in-creased circulation, which is a normal phenomenon ; but the increased circulation of a disturbed function is abnormal and pathologic. It leads to stagnation, dilatation of vessels, with es-cape of lymph and, if sufficiently strong and long continued, leads eventually to inflammation.

An additional reason why cold may have an influence for harm upon the respiratory organs in the case of its long continuance, at any rate, is that the eliminative functions of the skin are in abeyance. Toxins circulating in the blood which usually find exit through the skin may seek elimination by way of the mucous membranes, which are thereby possibly irritated and injured.

The subject of the atmospheric influence in the causation of colds may be summarised as follows: The atmosphere as a universal inescapable environment has had always and still has a profound influence on all life. For the utilisation of this element in the. life processes, the respiratory organs were' developed. For the warm-blooded animals there is. a differentiation of function in these organs, in that the distal extremities (air cells) are concerned with the chemical; the proximal (erectile tissue) with the physical properties of the air.

An organ becomes sensitive to the forces of the environment to which it. is adapted, and in con-sequence is affected by alterations therein. The respiratory tract must therefore be affected by alterations in the atmospheric environment; and the nasal end of it, especially affected by alterations in its physical properties. It is exactly the physical properties of the air which are most variable, and therefore the nose has a great bur-den to adjust itself to these sudden and wide variations. That the nose, the most frequent site of colds, would be especially affected by changes of temperature and moisture, coincides with the generally accepted view that these are the kinds of changes in the atmosphere which especially produce colds. The nose is concerned with these physical properties not only as an organ of respiration but as an organ of heat regulation in conjunction with the skin. On account of the latter function it is brought into close relationship with the skin, through sympathetic connection, and this explains how it is readily affected by atmospheric impressions on the body surface.

Tinder ordinary conditions the nasal organ can adjust itself to variations in the physical properties of the atmosphere and perform its respiratory functions as a heat regulating organ, but it must be adversely affected and suffer in the event of unusual and unnatural relations between temperature and humidity.

Prolonged moderately low temperature, for example, is harmful because it affords no opportunity for wholesome reaction; excessive cold, be-cause it paralyses the mechanism of reaction; low temperature with very high humidity, because the determination of blood is not then altogether consistent with physiological function; the draft, because unnatural conditions exist, which hamper the skin and the nasal organs in the performance of their functions, and disturb the harmonious relation which should exist between them.

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