356 COLLOIDS IN BIOLOGY AND MEDICINE 



When we think of aquatic animals the idea of an integument 

 which can swell leads only to caricature. 



This does not mean that hair, feathers, etc., cannot take up any 

 water. We all know that wool and feathers absorb water from the air 

 and that hi very moist air they feel damp; in making hygrometers, 

 human hair, which expands with a certain degree of moisture and 

 contracts with dryness, is used. 



The skin may be preserved thousands of years on account of its 

 slight swelling capacity. In fact, we find the framework of plants, 

 cellulose and wood, in graves of animals or men in addition to 

 bones, and usually hair, hide and leather articles. 



The evaporation of water from the skin occurs not only as the 

 result of the secretory activity of the sweat glands, but there is also 

 an "insensible perspiration." As P. G. UNNA* 1 has shown in con- 

 vincing experiments, this may be either inhibited by fats or on the 

 other hand increased by enlarging the surface, as with powders, coat- 

 ing with gelatin, collodion, etc. (see p. 416). 



As in the case of other cell membranes, the saturation of the skin 

 with lipoids, especially with lanolin, is of the greatest importance. 

 W. FILEHNE and J. BIBERFELD * investigated the absorption capacity 

 of clean keratin structures (wool fibers, feather flues and human hair) 

 as well as such as were saturated with lipoids. As was to be expected, 

 substances soluble in fat (phenol, chloroform, etc.) were easily ab- 

 sorbed, whereas water and salts penetrated but slightly. This corres- 

 ponds with the animal experiments of E. OVERTON on amphibia and 

 of A. SCHWENKENBECHER * on doves and mice. The almost complete 

 impenetrability of the lipoid-saturated skin for salts is of the greatest 

 importance to the organism in maintaining its electrolyte content. 



[Internal Secretions. W. BURRIDGE, by his perf usion experiments 

 with calcium solutions of varying strength, has offered an explanation 

 of some of the activities of several hormones. Pituitary substance 

 apparently increases the response of the uterus and the heart to cal- 

 cium. Adrenalin has a two-fold activity on the heart, a primary 

 depressing or surface action and a secondary or deep augmenting 

 action. During the period of exalted cardiac activity the heart is 

 more responsive to calcium than previously. The factors involved 

 are the concentration of adrenin, the concentration of calcium in the 

 perfusing solution, and the state of the heart induced respectively by 

 adrenin and by calcium. Excitation is viewed as a coagulative 

 change produced by calcium in certain colloids. 



The effect of thyroid secretion is similar to that of alcohol, causing 

 the circulation to be maintained on what otherwise would be an 

 inadequate calcium tension in the perfusing solution. Tr.] 



