VIVIPAROUS ANIMALS. 413 
one or two, apertures. The teats are named, from their si- 
tuation, either Pectoral, Abdominal, or Inguinal. They, in 
general, exceed the number of young produced at a birth, 
but exhibit very remarkable variations, according to the 
species, and even among individuals of the same species. 
The milk is usually of a white colour, with various 
shades of yellow, differing remarkably according to the spe- 
cies. It is somewhat heavier than water, but boils and 
freezes nearly at the same temperature as that fluid. It 
slightly reddens vegetable blues. 
When allowed to rest, it separates into two portions, one 
of which, termed Cream, is the lightest, and forms a layer 
on the surface of the Skimmed-milk below. 
The cream consists of three ingredients, butter, cheese, 
and whey, in the following proportion in a hundred parts, 
of cow’s milk, butter, 4.5, cheese 3.5, whey 92.0*. It was 
of the specific gravity of 1.0244. ‘The skimmed milk yield- 
in a thousand parts, water 928.75, cheese, with a trace of 
butter, 28, sugar of milk 35, muriat of potash 1.70, 
phosphat of potash 25, lactic acid, acetat of potash, with 
a trace of lactat of iron, 6, earthy phosphats 0.30. Its 
specific gravity was 1.033. The salts of milk have been 
still more minutely investigated by C. F. Schwarz, who 
obtained from a thousand parts of cow’s milk, phosphat 
of lime 1.805, phosphat of magnesia 0.170, phosphat of 
iron 0.032, phosphat of soda 0.225, muriat of potash 1.350, 
lactate of soda 0.115 = 3.697. A thousand parts of wo- 
man’s milk yielded, phosphat of lime 2.500, phosphat of 
magnesia 0.500, phosphat of iron 0.007, phosphat of soda 
0.400, muriat of potash 0.'700, lactat of soda 0.300 =4.407 1. 
“ Berzexius’s Annals of Phil. vol. ii. p. 424, + Ibid. 
+ Annals of Phil, v. p. 41, 
