648 THE POPULAR SCIEITCE MONTHLY. 



chondrine, the proximate chemical element of cartilage ; nor for gela- 

 tine, nor for syntonine, the constituent of muscle ; nor for their nervous 

 or biliary substances ; nor for their amyloid matters, nor, necessarily, 

 for their fats. 



It can be esperimentally demonstrated that animals can make 

 these for themselves. But that which they cannot make, but must in 

 all known cases obtain directly or indirectly from plants, is the pecul- 

 iar nitrogenous matter proteine. Thus the plant is the ideal prolkr 

 taire of the living world, the worker who produces ; the animal, the 

 ideal aristocrat, who mostly occupies himself in consuming, after the 

 manner .of that noble representative of the line of Ziihdarm, whose 

 epitaph is written in " Sartor Resartus." 



Here is our last hope of finding a sharp line of demarkation between 

 plants and animals ; for, as I have already hinted, there is a border- 

 territory between the tAVO kingdoms, a sort of no-man's land, the in- 

 habitants of which certainly cannot be discriminated and brought to 

 their proper allegiance in any other way. 



Some months ago. Prof Tyndall asked me to examine a drop of 

 infusion of hay, j^laced under an excellent and powerful microscope, 

 and to tell him what I thought some organisms visible in it were. I 

 looked and observed, in the first place, multitudes of Bacteria moving 

 about with their ordinary intermittent spasmodic wriggles. As to the 

 vegetable nature of these there is now no doubt. Not only does the 

 close resemblance of the Bacteria to unquestionable plants, such as the 

 Oscillatoria?, and lower forms of ii^im^^, justify this conclusion, but the 

 manufacturing test settles the question at once. It is only needful to 

 add a minute drop of fluid containing Bacteria, to water in which 

 tartrate, phosphate, and sulphate of ammonia are dissolved, and, in a 

 very short space of time, the clear fluid becomes milky by reason of 

 their prodigious multiplication, which, of course, implies the manu- 

 facture of living Bacterium-stufi" out of these merely saline matters. 



But other active organisms, very much larger than the Bacteria, 

 attaining in fact the comparatively gigantic dimensions of -g-oVo ^^ ^" 

 inch or more, incessantly crossed the field of view. Each of these had 

 a body shaped like a pear, the small end being slightly incurved and 

 produced into a long curved filament, or cilium, of extreme tenuity. 

 Behind this, from the concave side of the incurvation, proceeded an- 

 other long cilium, so delicate as to be discernible only by the use of 

 the highest powers and" careful management of the light. In the cen- 

 tre of the pear-shaped body a clear round space could occasionally be 

 discerned, but not always; and careful watching showed that this 

 clear vacuity appeared gradually, and then shut up and disappeared 

 suddenly, at regular intervals. Such a structure is of common occur- 

 rence among the lowest plants and animals, and is known as a contrac- 

 tile vacuole. 



The little creature thus described sometimes propelled itself with 



