42 



♦ KNOWLEDGE ♦ 



[June 16, 1882. 



blossoms. The clovers (Tri/o!iiim) arc a more ditfioult Bot of pea- 

 flowere. They are distinguished by their clustered roundish heads, 

 strai^'ht, small pods, and often tubular flowers; but, amonj^ them- 

 selves, the differences are very minute. Everybody knows common 

 red or purple clover, however (T. pratense), as well as the little 

 cream-coloured Dutch clover (T. repens), and these must bo taken 

 as fixed )>oiuts for determining the others. Tlio beautiful crimson 

 clover (r. incarnatinn), grown in great fields of brilliant colour, 

 is also familiar to almost all of us. Very near purple clover 

 come three other rarer sorts: T. muri'd'miini, with heads of 

 the same type but much smaller flowers, and rigid, stiff 

 calyx teeth (the lowest larger than the others) enlarged after 

 flowering. T. sfriulum, a little shabby creeping plant, with 

 calyx-teeth shaped like a pin's point; and T. scabrnm, which is 

 T. marilimum much dwarfed, and trailing along tho ground. 

 Nearer to Dutch clover arc T. hybridum, with rather pinker 

 blo5soms, and no rootlets on the stem, as well as tho curious 

 T. stilterraneum, whicli buries its own S3ed in tho ground, 

 and which may be known by its reduced number of flowers 

 — seldom more than three in tho head — as well as by its abor- 

 tive central blossoms, which only grow out after the pods begin 

 to swell, looking then like little hard-pointed knobs in the middle of 

 the cluster. A totally different modification of the clover type is 

 represented by hop-clover (T. procunibeiis), which may at once bo 

 discriminated by its likeness to a hop : it has numerous small 

 yellow flowers, turned back upon the stalk as it fades, and forming 

 a sort of brown ball. T. mnii/s is the same type dwarfed, with only 

 some twenty flowers in each head, instead of fifty, or thereabouts, 

 as in the larger form. 



The only other clovers you are likely to find at present are 

 T. arviiise, easily known by its fluffy, downy, purplish-grey head, 

 made soft as wool by the feathery teeth of the calyx, and T. fratji- 

 /erum, a close relative of Dutch clover, but looking rather like a 

 strawberry as it fades. Tho remaining species are very local. 

 Lotus corniculatus belongs to a falsely trifoliate genus, for though its 

 leaves look like trefoils, there are really two more leaflets at tho 

 base of each footstalk, easily overlooked unless you are warned 

 about them. Its bright yellow flowers, with a sharp, pointed keel, 

 are known to everybody everywhere. Rest-harrow (Ononis 

 arvensis) has usually trefoil leaves, but sometimes tho side leaflets 

 don't grow ; it may bo recognised by its pink, sweet-pea flower 

 and its |)ointcd keel. The other herbs of the pea tribe have several 

 leaflets, or at least have not trefoil foliage. Lady's fingers 

 (Anthyllts vulneraria) may reatlily bo known by their woolly, 

 fluffy, weedy-looking heads of yellow blossoms, with a leaf 

 luidt-r each head. Sainfoin (Onohiychia sativa) has a long and 

 handsome spike of pitjk and white-streaked flowers, and no ten- 

 drils to the leaves. In the vetches and peas there are almost 

 always tendrils at the end of tho leaf-stalks, though sometimes 

 they are reduced to a fine (loint liko tho end of a needle. Only 

 three vetches arc now common — Vicia sepiutn, with a bunch 

 of purple flowers, each without a soparato stalk ; V. sativa, 

 with solitary red flowers ; and V. cracca, with a handsome spike of 

 variegated blossoms on long stems. They may all be discriminated 

 from the peas by their nnmerons small leaflets. In the true peas 

 (Lalhyrus), on the other hand, tho leaflets arc usually few and 

 large ; as in L. pratenai; with its short bunch of pale yellow flowers. 

 In two rarer instances, however, there arc no leaflets at all ; L. 

 Si-e'Aia, the grass pea, has tho leaf-stalk flattened ont exactly liko 

 a blade of grass, and bears pretty red flowers ; while L. aphnca has 

 the stipules (or wings at tho base of the leaf-sta'k) expanded into a 

 pair of large grccn leaves. Tho only shrubby pea-plants likely to 

 be at present flowering are tho dwarf gorso (true furze has now 

 poddcii), and the last stragglers of tho broom, both of which are too 

 familiar to need description. Thus a einglo family has run away 

 with all our space ; but it is better to learn this one well the present 

 year, and take un another hereafter, than to overlmrdcn the mind 

 with a lot of petty distinctions at once, few of which will be accu- 

 rately remembered. Study tho plants of this single tribe, study 

 th. ir leaves, thi'ir flowers, their pods, their seeds; compare them 

 all carefully with one another, and yon will have done more 

 good work in one month than if you learnt off, parrot-fashion, a 

 hundred lists of half-known and half-understood species. 



THE HISTORY OF TUBERCLE. 



IN ptirining his investigations, Koch made nse of material derived 

 from both human and animal sources. Kxamination of the 

 tuljerculous material deposited in the lungs and other organs, in- 

 variably led to the discovery of minute organisms possessing all tho 

 bacterial characteristics of bacilli, and necessitated the conclusion 

 that these forms of life are invariably present in such deposits. 

 In yciipg tubercle, the bacilli were naturally more easily recog- 



nised ; but in older material, es)iocially in suoh as was dis- 

 tinctly caseous, their presence could not always bo demonstrated, 

 although abundant evidence of their oxistenco was found at the 

 edges of such accumulations. In a multitude of cases of 

 general miliary tubercalosis, bacilli in incalculiiblo niunbors were 

 encountered in every affected situation ; and in effect it may 

 bo taken as a warrautablo conclusion that they inevitably accom- 

 pany the developmeut at least of tho disease. From this point, 

 however, to a demonstration that they aro also tho cause of the 

 degenerations which accompany their presence, is a considerable 

 leap, the taking of whicli could bo justified only on tho accumulation 

 of sufficient actual proof of the fact. It is the production of this 

 proof that constitutes Koch's principal claim to tho gratitude of the 

 BCiontifio world ; and tho manner in which it has bocn accomplished 

 must win for its author an amount of praise such as fow rocont per- 

 formances of a similar kind have merited. 



Naturallj', but one moans of supplying the needed demonstration 

 presented itself — viz., tho adoption of exporinionts on living animals. 

 For tho purpose, therefore, numbers of guinca-pig.s, rabbits, and 

 cats were operated on, with the result, in every case, of verifying 

 tho assumptions of tho experimenter. Uy directly transferring 

 tho ^tuberculous matter from diseased animals to healthy ones, 

 through inoculation, ho succeeded iu all cases in reproducing 

 the disease ; but inasmuch as this proceeding was open to tho 

 objection that tho transferred material might possibly contain a 

 virus to which contamination was due, rather than to tho presenoo 

 in it of microscopic organisms, it was modified liy tho introduction 

 of "cultivation" experiments conducted on a very exhaustive 

 scale. In this connection, perhaps, more than any other, must 

 wo especially admire the unceasing persovoranco of Koch's pro- 

 ceedings, and also unhesitatingly accept the results obtained from 

 them. After lengthy trials, he succeeded in devising a jiabulum in 

 which bacilli grew and reproduced with tho utmost freedom. At 

 tho same time he was enabled to delcrmino the conditions which 

 were favourable and essential to their development, thus arriving 

 at the important discovery that they glow only within a narrow 

 temperature range of 30° to 41° C. ; below the former, and above 

 42°, no increase took place even after the lapse of so long a period 

 as three weeks ; thus a most important distinction is to bo drawn 

 between the bacilli of tubercle and tho bacilli of anthiax, tho latter 

 readily continuing the processes of active life down to a teinporaturo 

 as low as 20° C. 



Preserving, then, his cultivation fluid at the appropriate tem- 

 perature, Koch sowed a speck of tuberculous matter, and from tho 

 generation of bacilli thus produced ho infected a second quantity of 

 nutritive matter, and so on, until in some cases tho cultivation 

 process was extended over as long as six months. The purified 

 bacilli so obtained could not, by any possibility, be accused of com- 

 municating any foreign virus ; and yet, when introduced into 

 healthy animals, they never failed to reproduce themselves in 

 incalculable numbers, and to set up all the symptoms of tuberculous 

 infection. To quote ilcliiiite examples of tho experiments made 

 in this direction, it may be mentioned that four gninea-pigs were 

 inoculated with bacilli of tlio fifth generation produced in fifty- 

 four days from tuberculous matter originally derived from a 

 human being. In each case, the infected animal sickened and 

 lost flesh, and being killed at tho end of thirty-two or thirty- 

 five days, strongly pronounced tuberculosis was found in every 

 instance. Tho situation chosen for the injection of infective 

 material was fonnd to exert no influence on tho result. Tho abdo- 

 men, tho anterior chamber of tho eye, and other places were 

 selected, with always the same ultiniato consequences ensuing j and 

 in cases where check experiments were tnado by injecting natural, 

 healthy blood serum into animals at the same time as others were 

 infected with cultivated bacilli, it was found that while tho latter 

 sickened and became tuberculous, tho former romriinofl unaffected. 



In another series of experiments tho sputum of jihthisical patients 

 was obtained and dried thoroughly for six or eight weeks. At tho 

 end of this time, being suspended again in solution and injected 

 into guinea-pigs, tho latter became rapidly emiiciati'd, and in every 

 respect similarly diseased to those animals directly infected with 

 bacilli obtained at once from tuberculous masses, or through 

 successive cultivations. The iniportanoo of this particular 

 observation will bo at onco apparent. It proves that hitherto 

 unsuspected danger lurks in tho neighbourhood 6f every 

 consumptive indivii^ual, and that ordinary piecautions are in- 

 Buflicient to protect susceptible persons from tho influence of such 

 producing agents of a dire and rapidly destructive disease. At the 

 same time it must be assumed that it is ossontial for the infective 

 bacilli to find their way into tho body under certain definite 

 conditions in order for their development and the production of 

 tubercnlous deposits to follow as a matter of course ; and it is on 

 these by no means insignificant points that further information 

 must be obtained by means of further experimentation. Were it 



