2G BLOOD CORPUSCLES. 



small beaker, and filtered. Common concentrated (commer- 

 cial) acetic acid is then added with agitation, until a drop of 

 the mixture, when examined under a low power, is seen to con- 

 tain granules. If too much is added, the precipitate is not 

 fine enough. The latter is then to be separated by careful 

 decantation, and suspended in a half per cent, salt solution as 

 before. It is well to dilute the liquid with its bulk of serum 

 before using it. c. Aniline Blue is dissolved in common me- 

 thylated spirit, and filtered. Water or salt solution must then 

 be added gradually, so as to obtain a fine precipitate, the 

 resulting liquid being mixed with serum as above, d. Fresh 

 Milk. 



If it is intended to watch the process of feeding, a small 

 drop of blood, to which one of the liquids above mentioned 

 has been added, is examined, either in the ordinary way, in the 

 case of amphibian blood, or on the warm stage if mammalian 

 blood is emplo3^ed. If our object is merely to observe corpus- 

 cles already fed, the liquids in question ma}* be injected either 

 into the jugular vein (of rabbits or guineapigs) or into the 

 abdominal vein (of frogs), care being taken to employ a suffi- 

 ciently large quantity. After 10-30 minutes, a drop of blood 

 may be taken for examination. (See Chapter VII., as to in- 

 jection into the veins, and Chapter VIII., as to the lymphatic 

 sj'stem.) Whichever plan is adopted, it is alike possible to 

 satisfy ourselves that the cells not only take in foreign bodies, 

 but that they also have the faculty of discharging them, and 

 further, that when one cell comes into contact with another, it 

 often gives up to it the solid bodies which it has itself before 

 ingested. In general, the tendenc}* to ingestion varies with 

 the activity of the amoeboid movement, for the first thing 

 observed is an adhesion, either of the surface of the central 

 part of the corpuscle, or of a process to the foreign body, fol- 

 lowed bj r a retraction of the adherent part into its substance. 



Application of Liquid Reagents. It is, in the first 

 place, of importance to ascertain what liquids can be added 

 without affecting the vital phenomena of the colorless corpus- 

 cles. Such are designated by the adjective indifferent, and 

 are those which are always to be used in the study of fresh 

 living tissues. For example, we may use fresh serum or tran- 

 sudation liquids, as also the aqueous humour of the eye, which 

 has the important advantage of being entireh r free from formed 

 elements. The most commonly used indifferent liquid is the 

 half per cent, solution of common salt already mentioned, 

 which is of great value ; although, as may be readily under- 

 stood, it is not altogether without action on living tissues. In 

 the examination of blood, it is added as a preparatory step to 

 the addition of other reagents. With this view the solution 

 is dropped from a capillary pipette (Fig. 4) upon a slide ; a 



