50 



Chapter III 



very voracious animals and, among other things, devour the blood of 

 man or animals with avidity. One has merely to allow them to fast 

 for a few days, and then to give them a drop of blood in order to see 

 their digestive canal fill itself with this fluid 

 (fig. 6). The white Planarian, Dendrocoelum 

 lacteum, is well adapted for these researches. 

 In a worm that has sucked blood from a 

 Vertebrate, owing to its great transparency, 

 the whole length of its intestine with its 

 numerous ramifications may be seen. For 

 some time this organ remains of a bright 

 red colour, but gradually the tinge becomes 

 brownish or faintly violet. These changes 

 of colour recall those observed in effusions 

 of blood in or under the human skin result- 

 ing from contusions. A microscopical ex- 

 amination of Planarians that have been fed 

 with blood shows that the coloration of their 

 digestive canal is due to red blood cor- 

 puscles in different stages of digestion. Im- 

 mediately after the taking in of the blood by 

 the Planarian all the red blood corpuscles 

 are ingested by the epithelial cells of the in- 

 testine. Connected with the wall by slender 



[54] stalks, these elements appear as large amoeboid cells whose free end 

 projecting into the lumen of the intestine sends out protoplasmic pro- 

 cesses which seize the red blood corpuscles and convey them into the 

 interior of the cell. This goes on very rapidly, and in a very short 

 time all the red corpuscles are found within the epithelial cells. 

 As a result of the increase in volume of these cellular elements 

 the intestinal cavity is completely occluded. 



Once inside the cells of the intestine the red blood corpuscles 



[55] exhibit changes which are readily followed under the microscope. It 

 is better still to feed the Planarians with the blood of those lower 

 Vertebrates whose red corpuscles are nucleated. In my researches 

 I have used the blood of the goose. The red blood corpuscles 

 of this bird, when ingested by the epithelial cells of the intestine 

 of Planarians, are usually collected into compact groups (fig. 7), 

 only a few remaining isolated. The majority of these red corpuscles 

 soon lose their normal appearance and contour; they become 



FIG. 6. Young Planarian 

 some time after having 

 sucked goose's blood. 



