442 BLOOD AND LYMPH. 



opso'no, I prepare food for), which sensitize or in some way prepare 

 the bacteria so that they are attacked by the leucocytes. These 

 opsonins belong to the group of antibodies, and may be called 

 into existence or increased in amount by the injection into the 

 body of suitable bacteria or their products.* (2) They aid in 

 the absorption of fats from the intestine. (3) They aid in the 

 absorption of peptones from the intestine. (4) They take part 

 in the process of blood coagulation. (5) They help to main- 

 tain the normal composition of the blood-plasma in proteins. The 

 blood proteins are peculiar, and they are not formed directly from 

 the digested food. It is possible that the leucocytes, which are 

 the only typical cells in the blood, aid in keeping up the normal 

 supply of proteins. From this standpoint they might be regarded 

 in fact as unicellular glands, the products of their metabolism 

 serving to maintain the normal composition of the blood-plasma. 

 The formation of granules within the substance of the eosinophiles 

 offers a suggestive analogy to the accumulation of zymogen 

 granules in glandular cells. 



Physiology of the Blood Plates. — The blood plates are disc- 

 shaped bodies which appear as short rods or as circular or elliptic 

 plates, according as they are seen on edge or on the flat face. 

 They vary in diameter on the flat face, but are in all cases much 

 smaller than the red corpuscles. When removed from the circu- 

 lating blood they are known to disintegrate very rapidly. This 

 peculiarity, in fact, prevented them from being discovered for a long 

 time after the blood had been studied microscopically. It has been 

 shown that they are formed elements, and not simply precipitates 

 from the plasma, as was suggested at one time. The theory of 

 Hayem, their real discoverer, that they develop into red corpuscles 

 may also be considered as erroneous. There is considerable evi- 

 dence to show that in shed blood they take part in the process of 

 coagulation. The nature of this evidence will be described later. 



On account of their small size the structure of the blood plates 

 is not satisfactorily known. Deetjen* has demonstrated that they 

 are capable of ameboid movements. When removed from the 

 blood-vessels to a glass slide they usually agglutinate into larger 

 or smaller masses, swell, and disintegrate, but if received upon a 

 surface of agar-agar which has been made up with physiological 

 saline, together with some sodium metaphosphate (NaPOg), they 

 flatten out, show a central granular portion and a peripheral clear 

 layer, and may make quite active ameboid movements. The origin 



* For a brief general discussion of opsonins, see Hektoen, "Science," 

 Feb. 12, 1909. 



t "Virchow's Archiv f. path. Anat. u. Physiol.," 164, 239, 1901, also 

 "Zeitschrift f. phvsiol. chemie," 63, 1, 1909. 



