THE URINARY TRACT 265 
of 110. There is more uniformity in size than in the 
mammalian organ. 
Supporting tissues between the tubules seem less 
definitely nuclear in the bird than in the mammal, at least 
in so far as connective tissue is concerned, there being in 
the former only a few groups of mononuclears to be seen 
in the cortex. Perivascular tissues are reasonably rich. 
The epithelium of proximal and distal tubules is not 
easily fixed by our customary laboratory techniques, the 
best results being obtained by Zenker's fluid. As seen in 
a routine specimen of a normal organ it is vacuolated or 
very palely stained. The individual cells stand out clearly 
and many present a pointed end to the tubular lumen. 
Kidney Weights. 
According to the work of Mangan(4) and of Alezais(5), 
the bird has an average kidney-to-body weight of 6.9 
grams per kilo while man has a ratio of 4.3 grams, dog 5.9 
grams and guinea-pig 8.5 grams. The first author would 
show that the fisheating birds have the heaviest and vege- 
tarian birds the lightest organ. Our own figures are 
limited to the weights of apparently normal organs in 
thirty-one mammals and five birds ; they are as follows : 
per kilo of body weight 
Primates (5) 
7.7 grams 
Carnivora .... (6) 
7.6 grams 
Rodentia (2) 
15. grams 
Hyracoidea. . .(1) 
7.5 grams 
Ungulata (9) 
3.5 grams 
Edentata (1) 
5.6 grams 
Marsupialia.. .(7) 
7.6 grams 
Monotremata. (1) 
11.2 grams 
Average 7. 
Steganopodes . (1) 
9.1 grams 
Anseres (1) 
3.9 grams 
Struthiones. . . (3) 
7. grams 
Average 6.7 
This to be sure is not a very exhaustive list but is the 
result of our routine observations and subject to all limi- 
(4) Bull. Mus. Hist. Nat., 1911, 493 and 1912, 527, and C. R. Acad. 
8c. , 1.55, 182. 
(5) C. R. Soc. Biol, 1898, 5, 188. 
18 
