20S 



KN()\\Li;i)c.i: 



JuNi;. 1912. 



(lOi Tliosc wliicli fix atmDsplitric nitrof^'cn in tlit- 

 roots of ccTtain plants; the "nitr()-l)acti.Tia." 



(11) Tho fernient wliicli converts urea into ammo- 



nium carlionate, urease. 



(12) Those producing coloured substances from 



colourless chromogens. 



(!.>> Those whicli produce luminosity in certain 

 lowly forms of animal life: "hiciferase" 

 Mctini,' on the "luciferin." 



This list is b\' no means complete : it does not 

 include the putrefactive, or the various disease- 

 producing forms. But those mentioned are actively 

 engaged in the everyday life of some plant or animal. 

 In fact the whole vital field is occupied by them. 

 The meaning of the action of most of them is 

 sufficiently obvious : from our own personal point 

 of view the digestive are the most imjjortant. Were 

 it not for them our food would remain exactly as 

 swallowed, insoluble and unabsorbable : without 

 them we should starve though eating abundance. 

 Many tissue-ferments only just being recognised are 

 of immense importance. Take the case of a starving 

 man or animal. We sa\' in such a case the organism 

 "lives on" its muscle and on its fat ; but that explains 

 nothing. Endo-enzymes have been discovered which 

 dissolve the muscle and the fat of the body so that 

 soluble substances can get into the blood and thus 

 be carried to the heart and nervous svstem for their 

 nourishment. Hence after a period of starvation or 

 hibernation, the animal is found to be exceedingly 

 thin ; its tissues have literall}- been dissolved awa\'. 



The role of the putrefying and nitrifying ferments 

 is of the highest importance in the maintenance of 

 animal life, and in the continuous circulation of 

 nitrogen which goes on. .As soon as an animal is 

 dead, millions of bacteria set about dissolving its 

 tissues into a large number of different chemical 

 substances such as amides, amino-acids, ammonia, 

 compounds of sulphur, marsh gas, and certain highly 

 poisonous substances to which such names as 

 " cadaverine," " putrescine," have been given. Some 

 of these are gaseous and escape into the atinosphere ; 

 those containing nitrogen are attacked hv the nitri- 

 fying micro-organisms and con\erted into salts which 

 are utilised as the food of plants. The plants form 

 vegetable proteins which are eaten by hcrbiv^ora ; 

 man and the carnivora eat the herbivora — so that 

 " all flesh is grass." " Imperial Caesar dead and 

 turned to clay" does not remain "clay." His 

 imperial nitrogen undergoes many vicissitudes, and 

 may conceivably, in course of time, even become 

 part of the body of a descendant. 



The respiratory ferments believed to reside in tlu 

 depths of the tissues are exciting a good deal of 

 attention at the present time. It is now coming to 

 be believed that the tissues actually obtain their 

 oxygen from the blood by aid of a reducing-ferment 

 or "reductase" which hands o\cr the oxygen to an 

 o.xidase which applies it to the oxidation of the 



carbon and hydrogen of materials in the cells, with 

 the consequent liberation of heat. 



.\ i)articularly interesting ferment has lately l)een 

 recognised in certain coloured flowers: the beautiful 

 colour of a ])urple or pink sweet-iiea is due to the 

 interaction of achromogen with an enzyme. If either 

 one or the other is absent the flower is white; the 

 chromogen alone gi\os a white petal, so does the 

 enzyme alone. 



\\'e might now look into the various characters 

 possessed more or less completely b)- all ferments. 



The first characteristic common to them all is 

 that they cannot work in the absence of water. 

 Expressed chemically this is, that they act by 

 liydrol}-sis. The fungi and the bacteria, as well as 

 the enzymes, are quite inert when dried up. Veast 

 in a dry state will not ferment dry sugar : boots 

 must be damp to have the growth of green mould 

 on them ; it is because jam is moist that fungus 

 grows on it ; no perfecth' dry thing will decompose. 

 It was because it was sun-dried that Livingstone's 

 body was able to be preserved in Central .\frica and 

 brought to England for burial. 



The second characteristic is the excessively 

 minute quantity of the enz)-me which is able to 

 transform an enormous quantity of material acted 

 on (substrate). Thus one part of rennin, the milk- 

 clotting ferment, can clot four hundred thousand 

 parts of milk : one part of pepsine in seven hours 

 can digest five hundred thousand parts of fibrine. 



The third point is that the ferments, like true 

 catalysts, do not incorporate themselves with the 

 products of their activit\- : pepsine is recoverable 

 after it has peptonised. 



The fourth feature of ferments is their affectability 

 towards changes of temperature. .A ferment of 

 whatever kind can be active onl\- within a certain 

 range of temperature, and w ithin that range there is 

 a particular temperature at which the ferment works 

 most rapidly : this is called its " optiinum tempera- 

 ture." On each side of the optimum the ferment 

 works less and less energetical!}- or perfectl)'. .As 

 the temperature rises the ferment is inhibited, and at 

 last a temperature is reached at which it ceases to 

 work altogether. This is the destruction or "death" 

 temperature, the ferment w ill not work again under 

 any conditions. .\s one lowers the temperature from 

 the optimum, the ferment is similarly progressively 

 inhibited until it ceases to work altogether, but can 

 work again when the temperature is raised. 

 But no low temperature has been reached which 

 destroys ferments in the sense that a sufficiently 

 high temperature does. Professor MacKendrick 

 kept organisms of putrefaction for a hundred hours 

 at minus 8iX. — a temperature sufficient to freeze 

 alcohol — without killing them. Putrefaction was 

 arrested, but, on the temperature being raised, 

 became as acti\e as ever. Similarly, the late 

 Professor Macfad\en found that tlie temperature 

 of li(]uid air (minus 250"C) wnuKi nut kill certain 



