ZOOLOGY AND BOTANY, MIOEOSOOPY, ETC. 753 



of the protoplasm, which, is more intense than that of the solution 

 itself."* 



These ideas have been accepted without dispute until the last few 

 years ; it may even be said that they are still current in science. A 

 recent work, however, of Pfefferj seems destined to greatly modify 

 them. Whilst studying the osmotic phenomena in the lower plants, 

 and particularly in the Myxomycetes, he remarked that the mem- 

 branous layer of the protoplasm is soft enough during life to allow a 

 small crystal or a bacterium to pass through it without leaving a hole. 

 In this condition, on making an opening by means of a needle, the 

 whole protoplasmic mass may be seen immediately to show the colours 

 considered as exclusively characteristic of dead protoplasm. Now it 

 is known, at least amongst a great number of Thallophytes, that a 

 prick does not kill the protoplasm. Pfefifer concludes from this that, 

 whilst living, it is permeable by all the substances which colour it 

 after death ; but that the membranous layer, as long as it is entire, 

 prevents the introduction of certain of these substances into the 

 interior of the protoplasmic body. He founds this opinion on the 

 fact, observed by himself, that the peripheral layer becomes hard and 

 brittle as soon as the protoplasm dies. Any slight cause is then 

 sufficient to break through it, and consequently to allow the colouring 

 reagent to penetrate the protoplasm. But this does not take place, in 

 his opinion, when, after infinite precautions, the organism is killed 

 without injury to the membranous layer. Under these conditions, 

 those agents which do not colour living protoplasm will also not 

 colour it when dead. 



The possibility of colouring the central protoplasm of the Amoehce, 

 whilst the pseudopodia remain hyaline, seems to contradict the theory 

 of the German botanist ; but it must be observed that the pseudopodia 

 of the Amcehce, like the cilia of the Infusoria, are of the same nature 

 as the membranous layer of the protoplasm. It would therefore seem 

 that the latter behaves, in regard to colouring matters, in the same 

 way as with different mineral agents, admitting some and being 

 impermeable by others. 



To the first category belong cyanin or quinolein blue, eosin, 

 fuchsin, and anilin-brown. To the second the infusion of logwood 

 or saffron, solution of cochineal in weak acetic acid, and the ammoniacal 

 solution of carmine. 



The following is a list of the principal reagents in use for colouring 

 protoplasm : — 



Iodine — It is well known that iodine colours albuminoid substances 

 a dark yellow. Poulsen recommends its use in the following form for 

 colouring protoplasm a pale brown, and showing more easily the 

 bacteria and vibratile cilia of the micro-organisms. 



gr. 



Bisublimed iodine • 05 



Iodide of potassium 0*20 



Distilled water 16-00 



* Sachs, loc. cit., p. 39. 



t ' Pflanzenphysiologie,' 1. (1881) pp. 31 and 50. 



