With a view to pursue the mechanism eliciting low amplitude NMU voltage (L.A. NMU V.) and synchronization voltage (S.V.) which have a great significance in the electromyograms of Guillain-Barres syndrome (G.B.S.) and paralytic poliomyelitis and also to find out clues for the etiologic factor of G.B. the author performed the follwing experiments. Namely, inducing disease with the inoculation of agents isolated from infants with Guillain-Barres syndrome, such as coxsackie virus of A group type 2, Okumoto strain, the same type 19 Dohi strain and B group type 1 Saragai strain which mainly induce myositis, into young mice 15 days old, and also infecting polio virus type Ⅰ (Mahoney strain), type Ⅱ (Lansing strain), or type Ⅲ (mouse adapted Leon strain) into mature mice, the author compared the electromyograms from m. bicepus brachii, m. gasfrocnemius, and intercostal muscle of these mice, and obtained the following results. The test materials were 136 muscles from 32 young mice injected with coxackie virus (C. V.) and 191 muscles from 45 mature mice injected with polio virus (P. V.). 1. It has been verified that the electromyograms of normal young and mature mice, generally do not differ greatly from those of human with the exception of contact voltage, proving electromyographic experiments of mice are possible. In measuring the duration and amplitude of 374 and 492 action potentials of normal young mice and mature mice, and in the percentage histograms of each, the average duration has been found to be 4.69 ± 0.36 m. sec. in young mice, while 5.12 ± 0.11 m. sec. in mature mice; and the average amplitude to be 244.5 ± 7.36 μv and 252.3 ± 8.13 μv, respectively. In other words, both the average duration and amplitude are greater in mature mice than those in young ones. 2. L. A. NMU voltage has been recognized in 50 per cent of the mice injected with C. V. A-group strain, in 20 per cent of the mice infected wtih C. V. B-group strain, and in 27.2 per cent of total muscles examined, while on the contrary, in the mice infected with P. V. it has been found only in one mouse out of the twenty-two infected with Lansing strain and in 1.1 per cent of all muscles infected with P. V.. Conversely, synchronization voltage has been recognized in the mice infected with P. V. type Ⅰ, Ⅱ, or Ⅲ in 42.8, 54.5, and 22.2 per cent of respective group, and in 20.9 per cent of entire muscles examined, while S. V. can not at all be recognized in the mice infected with C. V. From these results it has been experimentally proven that L. A. NMU voltage is the abnormal electromyogram appearing mainly in the case of muscular disturbances, while S. V. is that appearing chiefly by lesions of the anterior horn of the spine. 3. The incidence of L. A. NMU V. observed in the young mice infected with Okumoto strain and that of S. voltage observed in the mature mice infected with Lansing strain both show a tendency to increase with the lapse of time. 4. The percentage histograms of the duration and amplitude of 234 action potentials obtained from young mice infected with Okumoto strain show a greater tendency of the shift to left than respective one observed in the normal young mice; their average values (2.8 ± 0.13 m. sec, and 155.1 ± 10.8 μv, respectively) are both smaller than those in normal young mice. And the differences in the average values of duration and amplitude are both statistically significant. 5. The percentage histograms of the duration and amplitude of 278 action potentials obtained from the mature mice infected with Lansing strain show a greater tendency of the shift to right than those of normal mature mice; and their average values (5.24 ± 0.10 m. sec, and 327.2 ± 20.8 μv, respectively) are both greater than those in normal mature mice. However, the difference in the average values of the duration is not statistically significant. 6. The pattern of L. A. NMU V. observed immediately after the crisis in C. V. infected mice often presents relatively interfering pattern, but it turns scanty with the lapse of time. From this fact it is assumed that the pathologic changes in nerve fibers are formed secondly. 7. In contrast to the opinion that the low amplitude NMU voltage appears in neurogenic atrophy as well as in myogenic atrophy, the author has verified that it mainly appears in myogenic atrophy. Furthermore, the author would put an especial emphasis on the fact that in the differentiation of myogenic atrophy and neurogenic atrophy not only numbers of frequenies of discharges but also the fluctuations in the duration should be taken into consideration. 8. From electromyographic findings obtained in the above-mentioned experiments and from those findings in G. B. syndrome reported previously in Part 1, it has been confirmed that Guillain-Barres syndrome is the disease accompanied by pathologic changes in muscles and the anterior horn of the spine.