ANATOMICAL ELEMENTS. 15 



in accord with the theory that the spleen, lymphatic glands and the bone- 

 marrow are always directly concerned in the production of leucocytes. 



Taking into consideration the histological and pathological observations 

 bearing on the question, the following seems to be the most reasonable view 

 with regard to the mode of development of leucocytes : 



1. In early foetal life the leucocytes of the blood are developed without 

 the intervention of any special organs, and perhaps, also, these bodies are 

 multiplied by division. 



2. In adult life the same processes of development probably occur in the 

 blood and lymph and in other situations. 



3. It is probable, though by no means certain, that the spleen, lymphatic 

 glands and the red marrow of the bones are more or less actively concerned 

 in the production of leucocytes, both under physiological and pathological 

 conditions ; but it is certain that these organs and parts are not the exclusive 

 seat of development of the so-called white blood-corpuscles and lymph-cor- 

 puscles. 



Uses of the Leucocytes. It is impossible, in the present state of physi- 

 ological knowledge, to assign any definite use to the leucocytes of the blood 

 and lymph. These bodies may be concerned to some extent in the develop- 

 ment of the red blood-corpuscles, but this view, which is held by many physi- 

 ologists, has no absolutely positive basis in fact. All that can be said is that 

 the office of the leucocytes has not been ascertained. Their action, however, 

 is important in the process of coagulation of the blood, lymph and chyle. 



Blood- Plaques. The so-called blood-plaques, described quite elaborately 

 by Bizzozero and others, have been long known to histologists, under a vari- 

 ety of names, such as globulins, elementary corpuscles, granular debris, gran- 

 ule masses, hgematoblasts etc. Until within a few years these bodies have 

 not been thought to be of much importance, and even now little is known of 

 their physiological and pathological relations. 



The blood-plaques in human blood may be easily observed, preparing the 

 blood by the following method (Osier) : 



" Upon the thoroughly cleansed finger-pad a single drop of the solution 

 is placed, and with a sharp needle, or pricker, the skin is pierced through 

 the drop, so that the blood passes at once into the fluid, which is then received 

 upon a slide and covered. The withdrawal of the corpuscles into the solu- 

 tion prevents the plaques from aggregating, and they remain as isolated and 

 distinct elements. The amount of blood allowed to flow into the drop must 

 not be large, and should be quickly mixed. In many respects the most suit- 

 able medium is osmic acid, one-half to one per cent, which has the advantage 

 that by its use permanent preparations can be obtained." 



The plaques are thin, circular discs, homogeneous or very faintly granu- 

 lar and of a pale, grayish tint. They measure TT J-oiF to nroinr (1'5 to ^'5 //.) 

 in diameter, about one-sixth of the diameter of the red blood-corpuscles. 

 They exist in the blood in the proportion of one to about eighteen or twenty 

 red corpuscles. 



In the circulating blood, the plaques are distinct ; but when the blood is 



