Ewart, The Relations of Chloroplastid and Cytoplasma. 291 



K n y states, that, in certain cases, chloroplastids, with a little 

 plasma attached, may continue to evolve oxygen for a time and 

 apparently assimilate. My own Observation was, that such were 

 less likely to show any evolution of oxygen, than ones which 

 were quite isolated (p. 426 A^) It is possible that what K ny observed 

 was a chemotaxic attraction of the Bacteria to the fragment of 

 dying plasma by the nutritious Juices exuding from it, this and 

 the presence of a certain amount of oxygen in the unringed pre- 

 parations permitting the movement of the Bacteria to continue for 

 a time in the neighbourhood of such fragments of plasma. (See. 

 pp. 366, 367, 418 A>). 



A fourth source of error arises from the fact that the illu- 

 mination employed by K n y was so intense that when any exami- 

 nations were made it must be weakened to avoid injury to the 

 eye. I have found that any concentration of the light, if ordinary 

 diffused daylight is used, beyond that afforded by a mirror and 

 Abbe condenser, soon reacts unfavourably upon the Chlorophyll 

 grain whether isolated or intact in the cell, causing finally a 

 diminution of their assimilatory powers, and a fading of the 

 Chlorophyll. (See. p. 439 A^ and p. 439—446 A*) 



At the some time concentrated Illumination, diminishes the 

 sensitivity and the rapidity of movement of the Bacteria andcauses them 

 finally to come permanently to rest. Both these results, are, as Frings - 

 heim and others have shown, rapidly produced if concentrated 

 sunlight is employed, but, in the tropics, even using the light directly 

 reflected from a cloud obliquely illuminated by the sun, with no further 

 concentration than by an ordinary microscope mirror and an Abbe 

 condenser, a similar, though much weaker, efFect may be produced, 

 if only the period of exposure be sufficiently long. It is extremely 

 probable that there are optimal and maximal as well as minimal 

 intensities of Illumination for assimilation (p. 447 A*) and if so, 

 there is no doubt but that, the optimal intensity of illumination 

 for assimilation, in the isolated Chlorophyll grain, will necessarily 

 be considerably weaker than when it is enclosed in a living cell, 

 forming part of an assimilatory tissue and thus partly shielded 

 from the light. 



In the few cases in which Kny and Kolkwitz used pure 

 cultures these were made on gelatine. I have found that such 

 cultures are not nearly as satisfactory as those made on bouillon- 

 agar. In the latter case only, can reliable cultures, of uniform 

 sensitivity at a given age, be obtained, which, when used, do not 

 cause the addition to the fluid employed of any of the waste pro- 

 ducts of Bacterial action, excepting CO 2, in appreciable amount. 

 The character, sensitivity, and motility, of the cultures, may be 

 markedly afFected by the medium on which they are grown, and 

 by the temperature at which they are allowed to develop. (See 

 pp. 365, 434 A\ p. 555 A^). The limits of temperature at which 

 cultures of B, termo, to be satisfactory, must be developed, are 

 from 20° C to 25" C. 



19* 



