CHAP, in.] ELIMINATION OF WASTE PRODUCTS. 671 



secretion of urine slowly returns, and the urine is then found to 

 be albuminous, remaining so for some little time. The serum- 

 albumin and globulin which could not pass through the intact 

 epithelium, can pass through when the epithelium is damaged by 

 interference with its nutrition. The appearance of albumin in the 

 urine (albuminuria) is a not infrequent symptom of kidney disease, 

 and its presence in other than minute quantities indicates imper- 

 fections in the glomerular epithelium. But even under unhealthy 

 conditions that epithelium still governs to a certain extent the 

 passage of material ; for the proteids of the blood-plasma do not 

 pass through bodily or in a proportion which corresponds either to 

 the relative proportion in which they exist in the plasma or to the 

 relative ease (or difficulty) with which they pass through mem- 

 branes. Though the " albumin " of albuminous urine frequently 

 consists of both serum-albumin and globulin, these do not neces- 

 sarily occur in the same proportion as in blood ; they vary in 

 urine much more than they do in blood ; and indeed the one or 

 the other may be absent ; moreover fibrin factors are very rarely 

 found. 



Hsemoglobinuria, or the presence of hemoglobin in urine, 

 may be brought about by injecting into the blood vessels laky 

 blood, or some substance such as pyrogallic acid, which will " break 

 up " the corpuscles of the blood. Now in such cases there is 

 evidence that the hemoglobin passes through the glomeruli; 

 minute disc-like masses of haemoglobin, the so-called 'menisci,' 

 are, by appropriate methods of preparation, found in situ in the 

 capsules. Such a passage is very far removed from being a 

 process of ditfusion. 



We may conclude then that the passage of material through 

 the glomeruli, like the transudation of lymph and even to a more 

 marked extent, is a complex affair in which the ordinary physical 

 processes of diffusion and filtration may play their part, but are 

 not masters of the situation. 



418. The work of the epithelium of the tubules. As we have 

 said the structural features of the epithelium cells of the tubules 

 seem to justify the conclusion that they exercise a secretory 

 activity comparable with that of a salivary or a gastric gland. 

 But their work is in many ways peculiar. In the case of the 

 salivary, gastric, and pancreatic glands there can be no doubt that 

 the specific constituents of the several secretions, mucin, pepsin, 

 trypsin and the like, are manufactured in the alveolar cells out of 

 antecedents of some nature or other. The evidence, as we have 

 seen, is all against the view that these glands merely withdraw, 

 secrete in the old sense of the word, from the blood these 

 substances preexisting in the blood. When the salivary glands are 

 extirpated or the pancreas or the stomach removed there is no 

 accumulation in the blood of the specific constituents of the corre- 

 sponding secretions. So also when the liver is extirpated there is 



