NATURE AND CONDITIONS OF LIFE. 9 



in the interior is often capable of rotation as a whole, or of 

 exhibiting an active circulation of granules similar to that ob- 

 served in many masses of animal protoplasm. Moreover, the 

 researches of Mr Francis Darwin have shown that the cells of 

 the glandular hairs of the Common Teasel (Dipsacus sylvestris) 

 emit mobile filaments of protoplasm quite similar to the " pseu- 

 dopodia " of many of the lower animals ; while wall-less masses 

 of protoplasm, capable of emitting pseudopodia, are met with 

 in the life-history of some of the lower plants. 



In speaking, however, of the power of nutrition and repro- 

 duction, or of the power of emitting pseudopodia, or of exhib- 

 iting irritability as being " vital properties " of protoplasm, a 

 fallacious mode of reasoning is employed. These powers 

 belong to living protoplasm, and it remains to be shown that 

 they are even potentially present in dead protoplasm as pro- 

 toplasm. At any rate, they stand in a different category to the 

 physical and chemical "properties" of protoplasm, since we 

 must suppose these to be invariably and constantly present in 

 protoplasm, whether alive or dead ; unless we are to deny that 

 protoplasm is a definite compound at all. 



Apart from this, however, we may admit that protoplasmic 

 matter * is " the formal basis of all life " (Huxley) ; and that 

 the phenomena of vitality cannot be manifested save through 

 the vehicle of protoplasm. Nevertheless, there remain certain 

 conditions equally indispensable to the external manifesta- 

 tion of vital phenomena j though life itself, or the power of 

 exhibiting vital phenomena, may be preserved for a longer 

 or shorter period, even though these conditions be absent. 

 These extrinsic conditions of vitality are, firstly, a certain tem- 

 perature varying from near the freezing-point to 120 or 130; 

 secondly, the presence of water, which enters largely into the 

 composition of all living tissues; thirdly, the presence of 

 oxygen in a free state, though some of the lower forms of 

 vegetable life are capable of existing in an atmosphere devoid 

 of oxygen. 



The higher manifestations of life are not, as a general rule, 

 possible unless all the extrinsic conditions just mentioned are 

 carried out, and the non-fulfilment of any of them generally 



* It has not yet been shown that the living matter which we designate 

 by the convenient term of "protoplasm " has universally and in all cases 

 a constant and undeviating chemical composition ; and there is, indeed, 

 reason to believe that this is not the case. It is also certain that there are 

 other materials, the exact use of which we do not at present know, which 

 are absolutely essential to the maintenance of life, probably even in its 

 humblest manifestations. 



