RELATIONS OF THE AIR TO OUR CLOTHING. 665 



feels the cold. It is the same with the hair of animals, and the feath- 

 ers of birds, they are also without nerves. 



Id pi-oportion as our heat-losses increase, while the creation of heat 

 in our interior remains about the same, we feel the necessity of dimin- 

 ishing the rate at which the heat leaves our immediate neighborhood. 

 This kind of regulation is somewhat taken care of involuntarily even 

 by the naked body. In consequence of the cold, the nerves which 

 act on the calibre of the blood-vessels of our surface contract them, 

 and lessen the quantity of blood in them, so that less heat comes to 

 the surface, and we need not be afraid of becoming also inwardly 

 colder if we feel cold, even very cold. 



The sensation of cold on the skin does not necessarily give the 

 measure of our internal temperature. In the cold stage of ague, for 

 instance, the temperature of the internal organs rises considerably, 

 while by a kind of spasmodic contraction of the superficial blood- 

 vessels the flow of heat toward the skin is less than normal. The 

 above-mentioned regulation of heat-loss by the capillary system of 

 our skin is not all-sufficient either in point of time or degree. The 

 cold may be too strong, and the regulator get overworked and para- 

 lyzed, so that additional clothing is required to delay the departure 

 of our heat, and to spare the nerves of the blood-vessels. We help our- 

 selves by additional clothing, and the underlying article of clothing 

 stands in the same relation to the outer one as the skin to its first 

 covering. From this point of view you have to consider the sequence 

 of shirt, under-clothing, coat, overcoat, etc., etc., an arrangement by 

 which we save the vasomotor nerves the greater part of their work. 



It is an open question, which the incompleteness of our hygienic 

 knowledge prevents us from answering quite satisfactorily, how far 

 we ought to hand over the regulation of our heat-loss to our dress, or 

 how far we should go in deputing it to our organism, and its capabil- 

 ity of transferring more or less heat from the centres to the surface of 

 our bodies. This self-help of the organism and the readiness for it re- 

 sulting from frequent exercise of this function are generally called hard- 

 ening one's self; the contrary, making one's self tender. The former we 

 can never quite dispense with, but I believe that too high a value is 

 sometimes put and too large claims made on it. One ought to possess the 

 capability and the readiness, but not to make use of them continually. 



All human aim must be to obtain the greatest effect at the smallest 

 expense. We ought to choose those means which attain the end with- 

 out exhausting our power, which should be preserved for higher pur- 

 poses. These principles ought to guide us in approaching the question. 

 It is not only superfluous, but positively injurious, to use one's self up. 



I believe that it is now evident to you that a part of the heat of 

 our body radiates from the surface of our clothing ; but we must now 

 consider whether this radiation does not vary according to the nature, 

 quality, or color, of the material. Experiments which have been 



