208 



NATURE 



[August 12, 1909 |] 



of the changes in which they can take part. Some of 

 these carbon analogues are closely related to those which 

 are concerned in building up organised structures of plants 

 and animals. 



All theories of life assume that its phenomena are in- 

 separably associated with certain complex combinations of 

 the elements carbon, nitrogen, hydrogen, and oxygen, with 

 the occasional aid of sulphur and phosphorus. These are 

 the elements of that protoplasm which is the physical basis 

 of life, and by their interplay they form the unstable and 

 complicated groupings of which that remarkable material 

 is composed. All the phenomena we call vital are 

 associated with the change of some protoplasm, and the 

 oxidation of carbon and hydrogen ; but it is quite open to 

 question whether the connection of life with the elements 

 first specified is inevitable. We can conceive the exist- 

 ence of similar groupings of other analogous elements 

 forming other protoplasms capable of existing within 

 much greater ranges of temperature than any plants or 

 animals now known to us have to withstand. For ex- 

 ample, we can imagine a high-temperature protoplasm in 

 which silicon takes the place of carbon, sulphur of oxygen, 

 and phosphorus of nitrogen, either wholly or in part. In 

 fact, protoplasm, so far as we know it in purest form, 





^'iljSjir^ 



always contains some sulphur, and often a little phos- 

 phorus, representing a very partial substitution of the kind 

 in question. 



In view of our newer knowledge there is, therefore, 

 nothing very far-fetched in supposing that under suitable 

 conditions a plant or an animal organism may be able to 

 construct from silicon compounds, ultimately derived from 

 the soil, something akin to silicon protoplasm for use in 

 its structures. 



Vou will now ask me whether there is any evidence 

 that anything of this kind actually occurs in nature. I 

 think there is, although I admit that the evidence is not 

 very varied so far as we yet know. 



First, as to the vegetable kingdom. It is well known 

 that many plants take up silicon in some form from the 

 soil, and use it in ways which my botanical friends tell 

 me they do not at present understand. Silicon is present 

 in the straw of cereals, such as wheat, oats, &c., and in 

 niost of the Graminea?. It w^as supposed that the' stiffness 

 of the straw was secured by a siliceous varnish, but this 

 view is not now in favour, 'as it has been found possible 

 to remove silica from the straw by careful treatment with- 

 out diminishing its rigidity. It is also present in the 

 NO. 2076, VOL. 81] 



leaves of some palms, for my friend. Dr. Hugo MiiUer, ia 

 the course of his extensive researches on the sugars present 

 in certain palm leaves, has been much troubled by the 

 presence in the extract from the leaves of siliceous com- 

 pounds of unknown nature. Again, a well-known sub- 

 stance called " tabasheer," consisting largely of hydrated 

 silica, including some organic matter, is obtained at the 

 nodes of some bamboos. What purpose silicon serves in 

 these plants, which seem to have special need for it, we do 

 not know, but the subject appears to be well worth closer 

 examination than it has yet received at the hands of plant 

 physiologists. 



I have on the table some good specimens of tabasheer, 

 and can show some portions on the screen which have been 

 rendered nearly transparent by soaking in benzene, and 

 under these conditions exhibit traces of structure. 



Next, as to the animal kingdom. The most satisfactory 

 evidence that we can at present offer as to the organ- 

 building capacity of silicon comes, curiously enough, from 

 some of the simpler organisms of the animal king- 

 dom, but the only group the short remaining time at 

 my disposal permits me to notice is that of the 

 sponges. 



You know that these curious forms of undoubted animal 

 life live in sea-water, and are usually anchored to rocks. 

 The sea contains a very minute proportion of silica in 

 solution, and the sponge has the power of appropriating 

 very considerable quantities in 

 the course of its life and as a 

 part of its normal food supply. 

 What does it do with this 

 silica? It appears to use Jt 

 in cell production, and from 

 the cell evolves the beautiful 

 and minute siliceous spicules 

 which are so abundant 

 throughout the structure of 

 many of the sponges. 



I have here some photo- 

 graphs of these spicules which 

 I have had taken, and shall 

 throw them on the screen. 

 Two of the best of them have 

 been made from microscopic 

 specimens kindly lent to me by 

 Prof. Dendy, who has made a 

 special study of these spicules 

 and of their modes of growth. 

 One of these slides is repro- 

 duced in the engraving 



(Fig- O- 



These structures do not re- 

 present mere incrustations, 

 but rather definite growths 

 from the cell protoplasm, and 



are themselves in the nature of cells of characteristic forms. 

 Prof. Dendy informs me that these spicules in certain cases 

 become surrounded by a horny substance and seem to die, 

 as if by cutting off the supply of energy as well as grow- 

 ing material. 



In some of the larger sponges, as in the beautiful 

 Euplectella aspergilliim, or " Venus' flower basket," re- 

 presented in Fig. 2, the siliceous material constitutes the 

 greater part of the sponge, as the soft portion resembles 

 a somewhat gelatinous coating from which the exquisite 

 siliceous structure is developed. 



To sum up, then, I have shown that silicon can easily 

 take the place of carbon in many nitrogen compounds, as 

 well as in others not including nitrogen. It therefore 

 seems to me that we hazard no very violent hypothesis in 

 supposing that the silicon which enters the sponge in its 

 food, probably as an alkaline silicate, is in the marvellous 

 animal laboratory made to take the place of a portion of 

 the carbon of the protoplasm from w-hich the spicules are 

 ultimately developed. 



The hypothesis is at any rate suggestive, and I hope 

 enough has been said to commend it to your consideration, 

 for there seems to be no doubt that silicon is capable of 

 playing a larger part as an "organic element" than we 

 hitherto had reason to suppose. 



Fig. 



