14 



KNOWLEDGE & SCIENTIFIC NEWS. 



[Feb., 1904. 



outside the ivory. Their lower tusks, however, are merely 

 functionless rudiments, often lost when the animals are 

 full grown. 



At the same time it is interesting to observe, that as 

 soon as the shortened chin and unsupported face had 

 become characteristic of the " mastodons," true elephants 

 with deep and ridged grinding teeth made their appearance 

 at least in the Indian region, and quickly spread over all 

 the Old World. The tusks of some species (rig. 4) now 

 grew to immense size. The cross-ridges of the grinding 

 teeth (fig. 5b) also became more numerous, and so much 

 deepened and compressed that they might rather be 

 described as plates ; while the inconvenient crevices 

 between them were filled for the first time with a third 

 kind of tooth- substance, which is rather soft, termed 

 cement. In the Lower Pliocene Stc/^odon, as the earliest 

 true elephant is named, large grinding teeth, consisting 

 of alternating cross-bands of hard and soft tooth-sub- 

 stance, were thus fully fashioned. 



The later elephants and those of the present day only 

 differ from each other in minor characters, and in the 

 degree of compression or multiplication of the plates of 

 their grinding teeth. The maximum complexity of tooth- 



Fig. 5a. 



structure is reached in some of the hairy elephants, or 

 mammoths (fig. 5) of the Pleistocene period, which ranged 

 far north, even within the Arctic Circle, and may often 

 have been compelled to feed on specially hard and dry 

 vegetation. Their grinders (fig. 5B) are much deepened, 

 capable of withstanding many years of wear in the mouth ; 

 and the numerous plates of which the posterior grinders 

 are composed would hardly be recognised as simple 

 tooth-ridges if all the initial stages in their evolution now 

 described were not forthcoming. 



The general conclusion, therefore, is that the history of 

 the elepliant is analogous to that of the other tribes of 

 hoofed animals which culminated in the horses and tiie 

 cattle. They ha\e grown from mere creatures of the 

 marshes to roam over the plains, or through forests, and 

 haveat the same time gradually acquired deeper and more 

 effective grinding teeth. For some inexplicable reason, 

 the lengthening of their legs with a concomitant shorten- 

 ing of their neck, necessitated a unitjue elongation of their 

 face and chin to reach the ground for browsing. When 

 this strange makeshift had reached its maximum degree, 

 the chin suddenly shrivelled, leaving the flexible, toothless 

 face without any support. By stages which we cannot 

 discover, because they concern only soft parts which are 

 never fossilised, tliis flexible face became the wonderful 

 prehensile proboscis of the elephants as we laiow them 

 to-day. 



The Latest Discovery 

 Concerning CoLrvcer. 



By J. T. Cunningham, M.A., F.Z.S. 



Whenever a startling discovery is made in science the 

 hope immediately arises that it may be applied to the 

 cure of the most dreaded of human diseases. X-rays 

 have been tried, and now physicians and patients are in 

 despair because radium cannot be obtained with sufficient 

 facility. But even if radio-activity is found to be capable 

 of checking the malignant progress of cancerous growths, 

 it is not likely to be more than a refined method of 

 cauterisation, a merciful substitute for the surgeon's 

 knife. No radical improvement in the treatment of the 

 disease is probable until we know more of its nature and 

 causes ; still less is it possible without such knowledge to 

 devise methods of prevention. The brilliant discoveries 

 of recent years have shown that many of the most 

 dangerous diseases are caused by infection, by the intro- 

 duction into the human body of infinitesimal organisms 

 of an animal or vegetable nature. Typhoid and tuber- 

 culosis, for example, are due to vegetable germs, malaria 

 to minute acti\e organisms belonging to the animal 

 kingdom, and in the latter case the disease is only com- 

 municated by means of inoculation carried out by mos- 

 quitoes. 



Numerous attempts have been made to prove that 

 cancer is also a germ disease, but the latest researches 

 tend to show that this view is erroneous. There is a 

 certain amount of evidence that cancer may be to a 

 certain degree infectious, but nothing to prove that the 

 contagion is caused by the transmission of a living germ 

 as in typhoid fever or malaria. The peculiarity of cancer 

 among diseases is that it consists in the rebellion and 

 malignant behaviour of certain parts of the body itself, 

 not in the attacks of foreign enemies. Cancer in fact is 

 a state of civil war in the body, a reign of terror pro- 

 duced by outbreaks of murderous fury on the part of 

 licentious revolutionists at one or more localities. 



The body is a complicated organisation of which the 

 ultimate units are microscopic cells, each cell being a 

 speck of living substance containing a central denser 

 particle called the nucleus. The cells are of different 

 shapes and sizes, and are united in various layers and 

 masses which constitute the tissues, such as the muscular 

 tissue, the bones, the brain and nerves, &c. Growth is 

 due to cell-division, one cell dividing into two, and each 

 of these two growing till it is again as large as the mother- 

 cell, from which it was produced. The fertilised egg from 

 which the body of any animal is developed is a single 

 cell, and the de\'elopment commences by the division of 

 this cell into two, which divide into four and so on. 



In this process of cell-division is manifested to the 

 microscopist a regular series of changes in the nucleus. 

 In its resting state the nucleus is a spherical structure 

 containing a network of delicate threads. In division 

 the spherical outline disappears and the network acquires 

 the form of a convoluted continuous thread. This thread 

 divides into a number of separate V-shaped loops, which 

 are arranged on the finer lines of a spindle-shaped figure. 

 Each loop divides along its length into two loops, and 

 one half of each loop passes to one end of the spindle, 

 the other to the other. This is the central event in cell- 

 division, by which one group of nuclear loops forms two 

 groups, and each of the latter forms a daughter-nucleus. 



Now it is a curious fact that the number of these 

 nuclear threads which appear at each cell-division is 



