July 19, 1888] 



NA TURE 



275 



that of leucin in the animal, and asparagin in the 

 vegetable— has been shown to be the work of such a 

 ferment in the two cases. These ferments, too, are inter- 

 changeable to a certain extent, for those of the alimentary 

 canal are capable of digesting the proteids of vegetable 

 bodies, while those of the latter can similarly split up the 

 animal albumins, fibrin, and other forms of proteid. 



The essential similarity of the metabolism is also indi- 

 cated by the appearance in the two cases of complex 

 bodies of somewhat similar constitution which are quite 

 comparable with each other. In the vegetable kingdom 

 these bodies are known as alkaloids ; in the animal they 

 have for the past ten years or more been known as 

 ptomaines. They are among the products of the destruc- 

 tive decomposition of proteids. Thus cadaverin, a body 

 found in putrefying animal matter, is apparently to be 

 looked upon as belonging to the same group cf bodies as 

 muscarin, the poisonous principle found in several species 

 of mushroom. 



Perhaps the latest development of the same idea has 

 been the discovery of ferments in the vegetable kingdom 

 which are comparable in their action with the rennet 

 which is obtainable from the stomach of many young 

 animals, particularly the calf. In an extract of such a 

 stomach taken while secretion of gastric juice is pro- 

 ceeding, or in the gastric juice itself, is a principle which 

 has the power of curdling milk — a property taken ad- 

 vantage of by the farmer in the process of manufacturing 

 cheese. The casein, which is the proteid concerned in 

 cheese-making, is, under appropriate conditions, converted 

 by this body into an insoluble form, which, for want of a 

 better name, may be called briefly cheese. The conver- 

 sion is not to be confused with the loose curdling which 

 takes place when milk becomes sour from putrefactive 

 changes or from the addition of an acid, for it is a true 

 coagulation, resembling the clotting of blood. Now, 

 recent investigations show us that in many plants a 

 similar ferment exists, which possesses an identical 

 power, producing, when added to milk, a clot which is quite 

 indistinguishable from that which is formed under the 

 action of animal rennet. The list of such plants is con- 

 tinually increasing, but they do not appear to be grouped 

 at all on the lines of the recognized natural orders. 

 Ranunculaceae, Solanaceae, Cucurbitacea;, Composite, 

 Galiacea?, and others, furnish us with conspicuous 

 examples. 



At a meeting of the Society of Natural Science of 

 Stockholm, held about four years ago, the Secretary 

 brought before the notice of the meeting the fact that 

 the common butterwort (Pinguicula vulgaris) possessed 

 the very curious property of causing a clotting of milk 

 when the vessels in which the milk was contained had 

 been first rubbed over with the plant. No explanation 

 was offered of the phenomenon, but a suggestion was 

 made that the power might be due to the presence of 

 micro-organisms. Judging from analogy with other 

 plants since discovered to possess the same property, it 

 is far more likely to be due to a specific unorganized 

 ferment. The occurrence of this in Pinguicula is very 

 significant, as bearing on the similarity of the metabolism 

 in animals and vegetables, for Pinguicula is one of the 

 carnivorous plants, digesting, by the aid of its secretions, 

 flies which it captures in its leaves. We have so asso- 

 ciated in the same plant a proteolytic and a rennet fer- 

 ment, a condition which at once recalls the gastric juice 

 of animals, in which both these bodies are present. 



One of the most interesting of the plants which con- 

 tain this ferment, or vegetable rennet, is the so-called 

 " Naras " of the West Coast of Africa (Acanthosicyos 

 Jiorrida), a species of Cucurbitaceae. The plant was 

 described in detail by Welwitsch, in 1869, when its 

 peculiar physiological property was unknown. A more 

 detailed description, given by Marloth, has recently 

 appeared, which deals, among other points, with this 



power. The plant is to be met with in dry, sandy, and 

 desert places in Namaqua Land, Whale Bay, and the 

 Mozambique district. It is very singular in its habit 

 and appearance, consisting of long, spiny, weak-looking 

 branches running almost on the surface of the sand, and 

 being at intervals buried therein and again emerging. 

 The stem is very short, so that the plant looks like a 

 system of creeping spiny branches, some of which mea- 

 sure 20 feet or more in length. The root system is similarly 

 developed, long creeping roots penetrating, in some 

 cases, for a distance of 100 feet through the sand. The 

 long spiny branches seem destitute of leaves, for these 

 are quickly deciduous and sometimes abortive, and while 

 they remain upon the shoots they are closely adpressed to 

 them, and are stiff and horny in texture. At the base of 

 each leaf are two strong spines, which persist after the 

 leaf has fallen. The flowers are borne in the axils of the 

 leaves, between the spines. The male and female flowers 

 are found on separate plants ; the former are sessile, the 

 latter shortly stalked. The ripe fruit is of considerable 

 size, much like an orange in appearance. It has a very 

 powerful and pleasant aroma, and its pulp is very juicy 

 and agreeable to the taste. In the unripe condition it is 

 bitter and uneatable. According' to Marloth, the natives 

 eat it to a very great excess, both fresh and in the form 

 of " Naras cake," a preparation of it made by drying the 

 expressed pulp and juice in the sun. The power to ap- 

 preciate its excellence seems to be confined to the natives 

 of the part, for strangers partaking of it for the first time 

 are said to pass through strange and painful experiences 

 after their banquet. 



Its power of causing the clotting of milk is well known 

 among the natives of the part, who use it freely for 

 that purpose. The ferment is contained in consider- 

 able quantity in the juice, the pulp, and the rind 

 of the fruit. It is absent from the branches, from 

 the seeds, and from all parts of the unripe fruit. It is 

 soluble, according to Marloth, in alcohol of 60 per 

 cent, strength, an extract of the pulp made with that 

 fluid retaining the power to coagulate the milk. It is 

 not identical with the principle which gives the frag- 

 rance to the ripe fruit, nor to that which gives the bitter 

 taste to it when still young. The ferment is destroyed 

 by boiling, but will remain for an almost indefinite time 

 in the dried rind. Marloth, in his experiments, found 

 that an extract of pulp dried to a friable condition in the 

 sun was quite active in causing coagulation. The writer 

 had the opportunity recently of examining some dried 

 rind and some old seeds. 1 An extract of these materials, 

 made with 5 per cent, solution of common salt, showed 

 the ferment in abundance in the rind, but absent from 

 both the testa and the interior of the seeds. 



Another plant, occurring nearer home, has the same 

 property. This is the common yellow Galium [G. 

 verum). In his " Popular Names of British Plants," 

 Prior speaks of its peculiarity as being known in the 

 sixteenth century, when Matthioli wrote of it, " Galium 

 inde nomen sortitum est suum quod lac coagulet." 

 In the West of England, particularly Somersetshire - 

 and Herefordshire, it is still the custom of dairymen to 

 put this plant into the milk they have devoted to cheese 

 production, to " set " it. The plant has a long straggling 

 stem, bearing at short intervals whorls of small leaves, in 

 the axils of which are numerous panicles of yellow 

 flowers. The practice is to put the whole plant, or as 

 much of it as is above ground, into the milk, but the 

 active principle seems to be located in the flowers. The 

 white Galium (G. Aparine) is said to be devoid of the 

 property. 



The common traveller's joy {Clematis Vitalba) is 

 another instance of the occurrence of this ferment. It is 

 peculiar in one respect, the property appearing to be 



■ This material was kindly furnished by Mr. W. Thiselton Dyer, F.R.S.. 

 Director of the Royal Gardens, Kew. 



