SECRETION AND EXCRETION 345 



He finds that they are caused by the clotting of fibrin when insol- 

 uble or difficultly soluble salts are simultaneously excreted. The 

 lamellation is caused by the repeated precipitation of fibrin with the 

 inclusion of crystalloid sediments. As many various experiments 

 showed, fibrin has a tendency to separate on surfaces, so that under 

 the conditions given, layers are formed. 



Sweat Glands. 



The daily excretion of sweat varies very widely. With the average 

 intake of water, average atmospheric temperature and at rest, it is 

 about 700 c.c. in 24 hours, in a man weighing 70 kilos (according to 

 A. SCHWENCKENBECHER). CRAMER found an excretion of 3 liters 

 during a summer march, and H. STRAUSS was able to establish a 

 loss of 1/2 to 1 liter of sweat in a half hour under the influence of 

 diaphoretic procedures. 



The sweat glands are more dependent on the influence of the 

 nerves than are any other glands, yet it cannot be doubted that here, 

 too, ultrafiltration of the blood plasma plays an important part, 

 since the sweat glands have a knotted structure similar to that of the 

 glomeruli of the kidneys. In support of this we have the following 

 facts: sweat contains only the solid constituents most easily per- 

 meable, NaCl and urea, whereas the difficultly diffusible salts, 

 phosphates and sulphates occur only in traces. The fact that 

 nitrogenous products of metabolism also occur, agrees with my 

 assumption that the NH 2 and NH 3 groups facilitate diffusion (see 

 page 411). The acid reaction is probably due to the sebaceous 

 glands; when the secretion is artificially increased, the sweat be- 

 comes alkaline (corresponding to the blood plasma) . 



Milk. 



Of all foods, milk is the most important; on this account it has 

 been investigated by food chemists and physicians. Its specific 

 gravity, fat content, dried fat-free residue, and even the casein and 

 albumin content and the quantity of milk, sugar and salts (ash) 

 have been determined, but it is only in the last few years that the 

 important part played by the condition of the colloidal constituents 

 has been pointed out. 



Milk is an aqueous solution of crystalloids (salts and milk sugar) 

 which contains the colloids, casein and albumin, and also an emulsion 

 of fat. 



Though the colloid constituents and the fat of milk vary within wide 

 limits according to food, season, age, etc. (from 5 to 8.585 per cent), the 



