264 COLLOIDS IN BIOLOGY AND MEDICINE 



E. KiisTER has called attention to numerous rythmic phenomena 

 among plants in which the influence of external forces cannot be 

 recognized and which consequently he attributes to LIESEGANG'S 

 law. Among others we may mention the thickening of membranes 

 in vessels and tracheae, the bands in striated portions of plants (herbs, 

 pinus Thunbergii Parl.), and the rhythmic changes in many blos- 

 soms. Doubtless the number of instances where we may entertain 

 the idea of internal rhythms may be increased at will and it will be 

 the task of future investigators to determine the essential causes. 



A valuable contribution in this connection was made by M. MUNK 

 who studied the formation of fairy rings. When moulds are grown 

 on bread, nutrient agar, etc., we frequently observe growth in con- 

 centric rings which suggest LIESEGANG'S layers and are popularly 

 called fairy rings. 



M. MUNK demonstrated that the accumulation of metabolic 

 products interfered with growth, causing a zone where there was but 

 little mould. In the case of some strong acid producing moulds 

 the distance between the individual rings may be regulated by the 

 addition of alkali to the nutrient medium. If litmus agar is used the 

 blue and red rings make visible the cause of the ring formation. 



It is interesting that layered structures in the ends of the periph- 

 eral nerves, which were looked upon as real, have been proved to 

 be artefacts. GOLGI stained nerves by saturating them with potas- 

 sium bichromate and then treating them with silver nitrate. He 

 obtained stratified structures whose appearance, as H. RABL showed, 

 changed with the concentration of the solutions, and they could be 

 nothing other than Liesegang's rings. 



Biological Growth. 



The fertilization of the egg is evidently the cause of the powerful 

 swelling processes, which are possibly induced by the formation of 

 acids. According to JACQUES LoEB,* 3 oxidation processes accompany 

 the development of the egg (whether fertilized or parthogenetic) ; 

 without oxygen no development of the ovum occurs. The increase 

 in the volume of the ovum of Echinoderma, until it reaches the 

 pluteus stage, is entirely conditioned by the absorption of water 

 (C. HERBST*). Before the larvae reach the pluteus stage they can- 

 not assimilate any organic nourishment. DAVENPORT* in the case of 

 frog embryos has shown that their dried weight remains the same 

 or diminishes till the moment when they commence to eat. Their 

 water content on the other hand was enormously increased. This 

 absorption of water is not due to an increase in the osmotic pressure. 



