DIMENSIONS OF BACTERIA 27 



An illustration of these forms is given in Fig. 3. According to a remark of 

 Emmerich's, these arcuate forms of growth are more especially abundant in 

 muciferous substances, e.g. in the excrement of snails, which is rich in mucin, 

 as also among the algae (already in a state of decomposition, and therefore 

 abounding in vegetable mucus) frequently covering the sides of drains and 

 watercourses. 



E. WEIBEL (I.) has published a series of observations on these forms of 

 growth, while fuller information concerning the spirilla frequently to be found 

 in the drainings from manure heaps can be obtained from KUTSCHER'S (I.) 

 treatise on this subject. 



When the longitudinal development is excessive, then the name of thread 

 bacteria is given to the cells, which are further distinguishable into the forms 

 to be noticed later ; Cladothrix, Streptothrix, Crenothrix, and Leptothrix being 

 described in chapter xxxiv., and Beggiatoa and Thiothrix in chapter xxxv. More 

 detailed notices of the Diplococcus, /Streptococcus, Pediococcus, Staphylococcus, and 

 Sarcina forms of growth will be found in chapter iv. 



28. Dimensions of Bacteria. 



Notwithstanding our previous statement that the bacteria are the smallest 

 of all known living organisms, it can be established that the differences (Fig. 4) 

 in their size hitherto observed must be characterised as very considerable. In 

 the smallest kinds the dimensions are under i /z, i.e. are less than o.ooi m.m. 

 For instance, the diameter of a lactic-acid-producing coccus examined by P. 

 Lindner was 0.6-1.0 p,. By way of contrast, mention may be made of Clos- 

 tridium butyricum, this bacillus measuring from 3 to 10 //. in length, with a 

 breadth of i p. The giants among the bacteria are to be found in the sub-group 

 of chromogenic bacteria, e.g. the genera Chromatiurn and Ophidomonas, which 

 have, therefore, formed the subject of exhaustive 

 investigation with regard to the internal construction 

 of the bacterial cell. 



We may here briefly allude to a fission fungus 

 which, although unimportant from a practical, techni- 

 cal point of view, forms, thanks to its large size, an 

 especially favourable object for the exhibition of pro- 

 portional dimensions, spore formation, &c., viz., the 

 Bacillus megatherium, found by DE BARY (I.) on 

 cabbage leaves. As the specific name would imply, 

 we have here an organism which excels in size all 



other fission fungi, as much as the prehistoric reproduction by fission. (After 

 Megatherium surpassed his contemporary congeners. De Bar y^ Ma &- 600. 

 This form is further illustrated in Fig. 5 ; the indi- 

 viduals h, r, k, I, will be described in chapter vi. (treating of spore germination), 

 so that only m and b need be considered at present. These are rods 2.5 p. 

 wide and 10 jj. in length, each of which would easily hold about ninety of the 

 previously described cocci. 



It will be useful to remember that the wave-length of light (corresponding to 

 the spectral line D) radiating from the sodium flame is about 0.6 yu, i.e. about 

 equal to the diameter of the above-named lactic acid coccus. Bearing this in 

 mind, the remark already made, that the smallest of the bacteria are almost 

 invisible, becomes comprehensible. 



FIG. 5. Bacillus megatherium. 



m. Two individual rods. 



b. Two rods at the moment of 



