CHARACTERS OF THE NUCLEUS 7 



unless special means are taken to preserve it, undergo more 

 or less speedy decomposition. 



Many of these properties of protoplasm can hardly be 

 verified in the case of Amoeba, owing to its minute size 

 and the difficulty of isolating it from other organisms (water- 

 weeds, &c.) with which it is always associated ; but there 

 are some tests which can be readily applied to it while 

 under observation beneath the microscope. 



One of the most striking of these micro-chemical tests 

 depends upon the avidity with which protoplasm takes up 

 certain colouring matters. If a drop of a neutral or slightly 

 alkaline solution of carmine or logwood, or of some aniline 

 dye, or a weak solution of iodine, is added to the w T ater con- 

 taining Amoeba, the animalcule is killed, and at the same 

 time becomes more or less deeply stained. The theory is 

 that protoplasm has a slightly acid reaction, and thus pro- 

 duces precipitation of the colouring matter from the neutral 

 or alkaline solution. 



The staining is, however, not uniform. The endosarc, 

 owing to the granules it contains, appears darker than the 

 ectosarc, and there is usually to be seen, in the endosarc, a 

 rounded spot more brightly stained than the rest. This 

 structure, which can sometimes be seen in the living Amoeba 

 (Fig. i, c, E, and G, mi\ while frequently its presence is only 

 revealed by staining (comp. A and B), is called the nucleus. 



But when viewed under a sufficiently high power, the 

 nucleus itself is seen to be unequally stained. It has lately 

 been shown, in many Amoebae, to be a globular body, en- 

 closed in a very delicate membrane, and made up of two 

 constituents, one of which is deeply stained by colouring 

 matters, and is hence called chromatin, while the other, 

 or achromatin, takes a lighter tint (Fig. i, F). The rela- 

 tive arrangement of chromatin and achromatin varies in 



