384 



The tbinl class of oi;j;:misms wliiih I woiiM ilistiiiguish has uo visible effect on 

 milk. This does not mean that tiny have in» eftect, for they giftw ra]ii«lly an«l ]>rfi- 

 duce various odors, iuditating that defomposition changes are going on in the milk. 

 The milk occasionally hecoun-s slightly aciil, sometimes slightly alkaline, and somt- 

 times the reaction is not affected. In no case, however, is the acid snflicient to 

 curdle the milk. * * * 



One of the most striking results of the growth of diti'erent bacteria in milk is the 

 character of the odors of the decompositions which an- produced. The subject is. 

 however, too intangible to describe. We have uo names sutlioient to enable us to 

 classify odors, uor have we sufficiently well-trained senses of smell to enable us to 

 remember a new odor foi* a long time. It is certain that the odors produced in the 

 dirt'erent milk cultures are widely varied and give plain indications of the forma- 

 tion of numerous volatile products, but I have been entirely unable to classify them. 

 These odors are important factors in producing the aroma of the butter which i> 

 niailc from the ripened cream. If it were possible to develop the discrimination 

 of this sen.se of smell, and to create a language to go with it, it is likely that a new 

 anil important factor could be ad<li'd to bacteriological investigations. * ' ' 



It will be seen that the j)hysiological action of the bacteria, as above outlined, 

 will explain all of the characters of ripened cream. The souring is due, of ccmrsc, ti> 

 the format inn of lactic acid by the acid-forming class of organisms. The slight 

 thickening is due to a more or less complete precii»itation of the casein in the form ol 

 a curd. The odor is due to a mi.xture of the vcdatile products of bacteria growth. 

 The peculiar aroma so im]iortant to the butter is due to the same cause. Tin 

 greater ea.se of churning sour cream is readily exjdained by the fact that either tin 

 a<"id formed by the bacteria or the trypsin-like ferment or both will tend to dissol\< 

 the protein mass (fibrin?) which we have seen ludds the fat globules together. Af> 

 soon as this tibrous mass is broken down the globules can more readily be shaken 

 together so as to fuse int<f large granules. 



Having readied this jtosition it bccdiiu-s flcsir.ible to study the effects ui>on butter 

 of rii)euing tlu' <ream with difiercut sj»eiies of ba<teri.i. If the right sjiecies ma.\ 

 In- found to be used as an artilicial feruient for the vipening process, this proees- 

 may be controlled, and if it can be cimtrolled the irregularity of butter making may 

 be eliminated. Exjieriments in tliis direction have been begun in connection with 

 the dairy of the experiment station. l)nt the work has not advanced far enough 

 at present to give any delinite results. 



A MICROCOCCUS OF BITTER MILK. II. W. ('(»NN.. I'll. \). (\)\). 158- 

 1()L'). — Niiu' Inini.s (»f bactt'iia wcir isolnicd tVoiii a sami>l«' of l)itti'r 

 (•Irani, ••oiH' of wliicli wa.s loiiml by siihst'([iu'iit expt'iiiiiciits to be the 

 cause (»1 the bitter taste." It is explaineil that the bitter taste in iiiilU 

 has IxM'ii supposed to Ite eoiiiie<*te<l with the Connatioii of butyric acid. 

 Weijiinaiiii. liowex er. lias recently conclitded that thr bitter taste is (bir 

 to a special liacilliis \vhi<'h he i.suhlted I'roni bitter milk, and wliicli. hr 

 says, does n(»t piotbice butyric acid. 



The author believes the organism isolated by hinisdl' iVcnu bitt«'r 

 creaiM tu be different from the one found by Wei;;mann in bitter milk. 

 The or.naiiism is described as "a ji(n»d-sized micrococcus, havini: 

 no teuih'ncy to form chains." It is immobile, white, ai'robian. ami 

 li(iueties i^elatin rajudly. the resultinji' li(piid beino- very slimy. Milk 

 iuocuhitetl with it — 



Curdled in one <lay in a warm oven. Becomes very bitter. Tin> liiinus solution 

 which is added to the milk turns slightlv red. Later the color of the litmus is 



