4 MANUAL OP ZOOLOGY. 



external shells of surpassing beauty and mathematical regu- 

 larity. In the face of these facts, we are therefore compelled 

 to come to the conclusion that life is truly the cause and not 

 the consequence of organisation ; or, in other words, that or- 

 ganisation is not an intrinsic and indispensable condition of 

 vital phenomena. 



Such an intrinsic and indispensable condition is, however, 

 according to Huxley, to be found in the presence of a uniform 

 ' physical basis,' to which he has applied the name of * proto- 

 plasm.' Without such a material substratum or medium 

 upon which to work no one vital phenomenon can be ex- 

 hibited. The necessary forces may be there, but in the ab- 

 sence of this necessary vehicle there can be no outward and 

 visible manifestation of their existence. Life, therefore, as 

 we know it, and as far as we know it, may be said to be in- 

 separably connected with protoplasm. 



As regards its nature, protoplasm, though capable of form- 

 ing the most complex structures, does not necessarily exhibit 

 anything which can be looked upon as organisation or dif- 

 ferentiation into distinct parts ; and its chemical composi- 

 tion is the only constant which can be certainly stated. It 

 consists, namely, in all its forms, of the four elements, carbon, 

 hydrogen, oxygen, and nitrogen, united into a proximate 

 compound to which Mulder applied the name of ' proteine,' 

 and which is very nearly identical with albumen or white-of- 

 egg. It further appears probable that all forms of protoplasm 

 can be made to contract by means of electricity, and ' are 

 liable to undergo that peculiar coagulation at a temperature 

 of 40-50 centigrade, which has been called "heat- stiffening." ' 

 (Huxley.) 



If we admit, then, with Huxley and the admission re- 

 quires some qualifications that * protoplasm, simple or 

 nucleated, is the formal basis of all life,' there, nevertheless, 

 remain certain conditions equally indispensable to the external 

 manifestation of vital phenomena ; though life itself, or the 

 power of exhibiting vital phenomena, may be preserved for a 

 longer or shorter period, even though these conditions be ab- 

 sent. These extrinsic conditions of vitality axe firstly, a cer- 

 tain temperature varying from near the freezing-point to 120 

 &r 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, this, like water, appearing to be a 

 sine qua non of life, though certain fungi are stated to offer 

 an exception to this statement. 



The non-fulfilment of any of these conditions for any length 

 of time, as a rule, causes death, or the cessation of vitality ; but, 



