224 



NATURAL SCIENCE. April, 



is at the mercy of accidental chemicals. Here is a case where a 

 change in the environment suppresses what nine out of ten biologists 

 would have called a fundamental character of the organism. 



It will occur, however, to most botanists that, striking as it is, 

 this tampering with the reproductive habit of an organism is by no 

 means novel. The yeast plant, for instance, and many of the higher 

 fungi, reproduce by spores only under definite conditions within the 

 power of an experimenter. It is familiar to all that the sexual ripe- 

 ness of flowering plants can be produced or suppressed by appropriate 

 environment. Even when the organs have been produced and 

 fertilisation has taken place, other definite conditions are necessary 

 for the production of seed. Moreover, in the special case to which 

 we have been referring, it would require more proof than Messrs. 

 Surmont and Arnould have supplied to satisfy us that a permanent, 

 and not merely a temporary, condition of asporogeny had been pro- 

 duced. In its present form, however, their experiment is a most 

 valuable addition to our knowledge of the plasticity of organisms. 



Animals in Sterilised Air. 



In these days it is chiefly the evil effects of bacteria upon or- 

 ganisms that are studied. Every week some new microbe of disease 

 is discovered, or some old enemies are described as lurking in some 

 unsuspected place. But there is another side to the microbe question. 

 It has been known for long that many kinds of bacteria, normally 

 present in the intestine, aid in the digestion of food, chiefly acting as 

 ferments, altering food-material into substances that can be absorbed 

 by the cells of the intestine. Dr. j. Kijanizin, of the University of 

 Kieff, gives, in a recent number of the Archives de Biologie (vol. xiii., 

 P- 339)> the remarkable results of a series of investigations he has 

 made upon the influence of sterilised air. He devised an apparatus 

 in which small animals could be kept for a number of days, while the 

 air that they breathed and the food that they ate were supplied, so 

 far as possible, in an absolutely sterilised condition. Although it 

 was not possible to be certain that the food contained no bacteria, it 

 was certain that the air supplied them had been quite freed from 

 microbes ; for a gelatine plate, placed in the current, remained 

 without colonies all through the experiments. The animals were 

 weighed before and after the experiments, and their excreta during 

 the experiment were analysed. Parallel experiments, in which all the 

 conditions but the sterilisation were identical, were made. 



The experiments seemed to show first that there was a remarkable 

 decrease in the assimilation of nitrogenous matter when the air and 

 the food were deprived of micro-organisms. No doubt, the reason of 

 the decrease was that these micro-organisms aid in the decomposition 

 and peptonising of the nitrogenous matter in the intestine. Were it 

 possible to remove all the micro-organisms from the intestine before 



