DIFFERENT ORDERS OF ANIMALS. 637 



and larger than in mammalia, yet larger in rep- 

 tiles, fishes, and other cold blooded animals than 

 in either.* The consequence of which is, that 

 their whole organization exhibits corresponding 

 variations. Nor is this more strange, than that 

 the form of crystals, and the chemical properties 

 of many bodies composed of the same ponderable 

 elements in the same proportions, should vary 

 according to the temperatures at which they are 

 produced, or the quantity of caloric around their 

 particles, and the number of atoms that compose 



* Hence it is, that when the blood of mammalia is injected into 

 the veins of birds, the latter die in a very short time ; and vice 

 versa while the blood of reptiles and fishes is rapidly fatal to all 

 the higher animals, in which the extreme capillaries are so small, 

 that they cannot be seen without a good microscope ; but may 

 often be discerned with the naked eye in cold blooded animals. 

 In regard to the colour of the red particles, nothing has been 

 clearly ascertained, except that it is owing to an envelope sur- 

 rounding white nucleii, from one-third to one-fourth the size of 

 the blood corpuscles, according to Hewson ; and which he sup- 

 posed to be identical with the white globules of chyle. Some 

 have referred their red colour to the presence of carbon, others 

 to iron or its oxide, because found united with the red particles, 

 (in the ratio of about 2 drs. to 30 Ibs. of blood,) or of 5-6 parts 

 of the pure metal in 10,000 parts of blood. But as both 

 of these substances are found in chyle, which is white, and as 

 many bodies are red without containing either, we must look for 

 some other explanation, connected more immediately with the 

 function of calorification. For it is evident that the depth of 

 colour is in proportion to the mean temperature of animals, being 

 brighter in birds than in mammalia, yellowish in reptiles, and still 

 paler in fishes, if we except the tunny tribe, (and a few others,) 

 whose breathing apparatus is very extensive for their class ; while 

 in animals of a still lower grade, it is without any colour. 



