THE VITAL PROPERTIES OF THE CELL 143 



may also be found distributed throughout the whole endoderm of 

 Actinia larvae after suitable feeding. 



But white blood corpuscles, lymph cells and the migratory cells 

 of the mesoblast, in both Vertebrates and Invertebrates, afford us 

 the best material for observation, in consequence of their power 

 of absorbing and digesting solid bodies. This important fact was 

 first observed by Haeckel (V. 4a), who injected a mollusc (Tethys) 

 with indigo, and found after a short time that indigo granules 

 were present inside the blood corpuscles. 



Metchnikoff (V. 12) has further investigated the phenomenon 

 most thoroughly. He found that if powdered carmine were injected 

 tinder the skin of another species of mollusc (the transparent 

 Phyllirhoe), the smaller granules were eaten up by some of the 

 migratory cells, while the larger ones attracted a number of other 

 migratory cells around them, which surrounded them like an 

 envelope, and fused themselves together to form a plasmodium 

 or multinucleated giant cell. 



That the same thing occurs in Vertebrates may be easily proved 

 by injecting some carmine into the dorsal lymph sac of a Frog, 

 and, after a short time has elapsed, removing some drops of lymph, 

 and examining them with the microscope. Further, the eating 

 process can be directly followed under the microscope if powdered 

 carmine or a little milk be added to some fresh drops of lymph or 

 of blood which have been carefully drawn off, certain precautions 

 having been observed. If the blood has been taken from man or 

 some other mammal, the preparation must be carefully heated on 

 Max Schultze's warm stage until it has attained a temperature 

 of 30-35 Celsius (V. 43). The white blood corpuscles now 

 commence to show amoeboid movements ; they seize with their 

 pseudopodia the carmine granules, or milk globules with which 

 they come in contact, and draw them into their bodies. On this 

 account Metchnikoff designates them as phagocytes, and the whole 

 process as phagocytosis. 



This capacity of the amoeboid elements of the animal to take 

 up solid substances is of great physiological importance ; for herein 

 the organism possesses a means of ridding itself of foreign and 

 noxious organic particles which are present in its tissues. There 

 are three different conditions of the body, partly normal and 

 partly pathological, when the phagocytes exercise this function. 



Firstly, during the process of development in many Inverte- 

 brates and also in Vertebrates, certain larval organs lose their 



