A STUDY OF THE BLOOD 



125 



*&& 



i't&t 



5. A COMPARATIVE STUDY OF BLOOD 



Animals without Blood. Anioebas and other single-celled 

 animals, as we have seen, have no blood. In the sponges, 

 sea anemones, and jellyfishes, also, there is no distinct tissue 

 that can be called blood, since absorption of food, respira- 

 tion, and excretion can be carried on throughout the whole 

 of the interior surface of these animals. All the other 

 groups of animals have 

 some kind of a circula- 



Color of the Blood. 



Many of the inverte- 

 brates (animals having 

 no backbone) have color- 

 less blood. There are, 

 however, exceptions to 

 the rule. In lobsters and 

 other so-called " shell- 

 fish," for example, blood 

 is bluish, while in worms 

 it is reddish, yellowish, 

 or greenish. In nearly 

 every vertebrate the 

 blood is red. 



Temperature of the 

 Blood. The body tem- 

 perature of a human being in health is 981 Fahrenheit, and 

 this is of course the temperature of the blood. In fever this 

 sometimes rises to 105 or even 109; in other diseases the 

 temperature may decrease a degree or more, but any greater 

 variations from the normal are usually fatal. In birds the 

 blood is about ten degrees warmer than it is in man (i.e. 

 108 F.). Keptiles (snakes, turtles, and alligators), am- 

 phibia (that is, animals living the first part of their life in 

 water and the adult period on land, for example, frogs and 



Fi. 45. Corpuscles of Frog's Blood. 

 Magnified about 50 times. Photographed 

 through a microscope. The oval disks 

 with the dark nuclei are the red corpus- 

 cles. In the center are the nuclei of two 

 white corpuscles of smaller size. 



