3i6 SCIENCE PROGRESS 



inorganic growth. Organic growth is clearly a process of 

 extreme complexity, one that involves the association by a 

 variety of operations of a whole series of diverse units. 



It is impossible to regard demonstrations such as Leduc has 

 given with silica and other simple colloids as in any way 

 comparable with the phenomena of organic growth. 



Moreover, Loeb's experiments are wrongly quoted by 

 Schafer as instances of sexual reproduction — what Loeb has 

 done has been to show that the life cycle may be started afresh 

 by the introduction of an excitant into the ovum and has thereby 

 shown that the process of fertilisation by the spermatozoon is 

 one in which at least two events are scored — the one being the 

 incorporation of male elements with female elements, whereby 

 biparental inheritance is secured ; the other the introduction of 

 an excitant (hormone) which conditions the renewal of the vital 

 cycle of the organism — but the development is that of an in- 

 complete being whose somatic cells lack half the normal 

 number of chromosomes. 



Three years ago, in my laddress to Section B of the British 

 Association at Winnipeg, I had the temerity to do what Sir 

 William Tilden says no chemist will be prepared to do — as 

 witness the following passage : 



" The general similarity of structure throughout organised cre- 

 ation may well be conditioned primarily by properties inherent in 

 the materials of which all living things are composed — of carbon, 

 of oxygen, of nitrogen, of hydrogen, of phosphorus, of sulphur. 

 At some early period, however, the possibilities became limited 

 and directed processes became the order of the day. From that 

 time onward the chemistry prevailing in organic nature became 

 a far simpler chemistry than that of the laboratory; the 

 possibilities were diminished, the certainties of a definite line of 

 action were increased. How this came about it is impossible to 

 say ; mere accident may have led to it. Thus we may assume 

 that some relatively simple asymmetric substance was produced 

 by the fortuitous occurrence of a change under conditions such 

 as obtain in our laboratories and that consequently the 

 enantiomorphous isomeric forms of equal opposite activity were 

 produced in equal amount. We may suppose that a pool con- 

 taining such material having been dried up dust of molecular 

 fineness was dispersed ; such dust falling into other similar pools 

 near the crystallisation point may well have conditioned the 

 separation of only one of the two isomeric forms present in the 

 liquid. A separation having been once effected in this manner, 

 assuming the substance to be one which could influence its own 



