42 PROTOPLASM 



in a drop made transparent by half-diluted glycerine and 

 strongly compressed, a diffusicnal exchange of fluid be set 

 up, either by adding concentrated glycerine, or by the 

 addition of water. Concentrated salt solution has also been 

 occasionally employed with good results. As has been said, 

 after some time one observes in places, or in successful pre- 

 parations over the whole surface of the drop, fine radiate 

 markings directed radially to the surface, which penetrate 

 more or less deeply into the froth-drop, sometimes even 

 to a considerable distance. The radial striation often 

 appears especially well marked round the larger vacuoles 

 of the interior, and it then attains not infrequently an 

 extension equivalent to the diameter of the vacuole. A 

 closer microscopic investigation of this radiate appearance 

 shows, that it depends on the meshes or alveoli being dis- 

 posed one behind the other in a more or less pronounced 

 radial arrangement. I have convinced myself of this in the 

 clearest manner, and the photograph (VI.) of such a radiate 

 structure, which is in my supplement to this work, also 

 shows this to some extent, although unfortunately it was 

 taken from a very defective preparation, and has not itself 

 come out particularly well. 



The conditions under which these radiate markings are 

 especially produced are of themselves a proof that diffusion 

 currents play a part in giving rise to them. I am not. able 

 to give more precise information as to the manner in which 

 the influence of the diffusion is expressed by them, but it 

 appears to me certain, as has been said, that the diffusion 

 between the contents of the alveoli and the surrounding 

 medium, or the contents of larger vacuoles, is the primum 

 movens in the process. 



A peculiar observation which I frequently made on oil- 

 drops appears to me to belong to this same category of 

 phenomena, and perhaps it throws further light on the 

 appearances already described in the foam-drops. In my 

 experiments I often used oil evenly mixed with a lamp- 

 black purified by extraction with alcohol, or by heating to 

 the glowing point for some time. When .drops of such an 

 oil were brought into water, it could usually be very 



