DEVELOPMENT OF THE RED CORPUSCLES 21 



various derivatives of hemoglobin may be recognized by their absorption- 

 bands in the spectrum. Methemoglobin, formed by adding potassium 

 ferricyanide or amyl nitrite to the blood, contains the same proportion 

 of oxygen as oxyhemoglobin, but in a different form of combination 

 (see Plate II, Fig. 2). 



Precipitin-Test for Blood. A test for blood, which surpasses in 

 delicacy any known test for any known substance, depends on the 

 property of blood-serum, adapted to a certain species of animal, of 

 forming a precipitate when mixed with the blood of the adapted ani- 

 mal. This, it is said, will detect the presence of blood of a given 

 species of animal in the proportion of one part in fifty thousand. The 

 following illustrates the operation of this test : Repeated daily injec- 

 tions of human blood-serum are made into the peritoneal cavity of a 

 rabbit for seven or eight days. In this way the blood of the rabbit 

 becomes adapted to the human blood. A little blood-serum of the 

 rabbit is now to be mixed with a small quantity of a salt-solution of 

 the suspected blood. If the specimen is from the human subject or 

 one of the primates, the mixture will present an abundant precipitate. 

 If there should be no precipitate, it is certain that the specimen does 

 not contain human blood. 



DEVELOPMENT OF THE RED CORPUSCLES 



In the circular area that surrounds the embryo in the earliest stages 

 of development, called the area vasculosa, bodies make their appear- 

 ance that afterward take on the characters of the red blood-corpuscles. 

 In the process of formation of this area, nucleated mesoblastic cells 

 branch out in various directions to form a sort of network, which is 

 afterward changed into a connected system of vessels. Nucleated 

 bodies then collect in certain parts of this network, which become sur- 

 rounded with protoplasm and afterward are colored with hemoglobin. 

 At first there are no regular movements in the area vasculosa ; but a 

 rudimentary heart is soon formed by a twisting of the great central 

 vessel upon itself, and the currents of the circulation become estab- 

 lished. During this time the blood-cells are capable of ameboid move- 

 ments and undergo multiplication by karyokinesis. They are at first 

 white and nucleated, but soon become colored, the nuclei remaining. 

 These first-formed embryonic corpuscles (erythroblasts) measure g-gW 

 to Y5*oo" f an i ncri (10 AI to 1 6 p) in diameter. 



As the liver, spleen, thymus and lymphatic glands are developed, 

 they assume the function of producing red blood-corpuscles, which also 

 multiply by karyokinesis in the substance of these organs. In the foetus 



